Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ π -¹ ² ³ °

You are not logged in.

- Topics: Active | Unanswered

**mathgogocart****Member**- Registered: 2012-04-29
- Posts: 1,472

We will post prime numbers and say something intrssting about the number

So lets start

3!

the unluck number:|:|:|:|

Hey.

Offline

**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 15,955

2-the only even prime.

Here lies the reader who will never open this book. He is forever dead.

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

The knowledge of some things as a function of age is a delta function.

Offline

**mathaholic****Member**- From: Earth
- Registered: 2012-11-29
- Posts: 3,025

5-number of fingers on your hand!!!

Mathaholic | 17th most active poster | 681st most recent person to join MIFF | Person | rrr's classmate

Offline

**noelevans****Member**- Registered: 2012-07-20
- Posts: 236

7 One of the few primes whose reciprocal is easy to remember.

For 1/7: 2*7=14, 2*14=28, 2*28+1=57 ; that is, keep doubling the denominator till you reach

56 then add the numerator to the 56 to get the last two digits of 1/7 which is a repeating .142857.

Of course 1/2, 1/3, 1/5 and 1/11 aren't bad either.

Writing "pretty" math (two dimensional) is easier to read and grasp than LaTex (one dimensional).

LaTex is like painting on many strips of paper and then stacking them to see what picture they make.

Offline

**mathaholic****Member**- From: Earth
- Registered: 2012-11-29
- Posts: 3,025

13- number of different cards in a deck

Mathaholic | 17th most active poster | 681st most recent person to join MIFF | Person | rrr's classmate

Offline

**noelevans****Member**- Registered: 2012-07-20
- Posts: 236

11 --- one of the few primes larger than 10 that it is easy to multiply by. To multiply a number, say

3142 by 11 just put a zero in front and behind it, like so 031420 and then add consecutive pairs of

digits (typically from right to left since in some cases there may be carries) and record these sums:

0+3, 3+1, 1+4, 4+2, 2+0 ; that is, 34562. If a sum exceeds 9 then carry 1 to the next sum for example 23572 ---> 0235720 ---> 2 5 8 12 9 2 = 2 5 9 2 9 2; that is, 259292 carrying the 1

from the 12 into the 8 in the next column to the left. With a little practice this can be done quickly

in one's head.

*Last edited by noelevans (2012-12-06 10:55:06)*

Writing "pretty" math (two dimensional) is easier to read and grasp than LaTex (one dimensional).

LaTex is like painting on many strips of paper and then stacking them to see what picture they make.

Offline

**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 15,955

19-the first prime with the sum of its digits equal to 10.

Here lies the reader who will never open this book. He is forever dead.

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

The knowledge of some things as a function of age is a delta function.

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 100,263

23

John Forbes Nash's favorite prime number.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.** **Thinking is cheating.**

Offline

**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 15,955

Boy, was that guy an ugly fellow!

97-largest prime below 100.

Here lies the reader who will never open this book. He is forever dead.

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

The knowledge of some things as a function of age is a delta function.

Offline

**mathgogocart****Member**- Registered: 2012-04-29
- Posts: 1,472

131-the number that is ALSO PSELLED BCAKWARDS...OMG

Hey.

Offline

**noelevans****Member**- Registered: 2012-07-20
- Posts: 236

13 --- a baker's dozen.

Writing "pretty" math (two dimensional) is easier to read and grasp than LaTex (one dimensional).

LaTex is like painting on many strips of paper and then stacking them to see what picture they make.

Offline

**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 15,955

23-number of characters in "greengrocers apostrophe"

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

The knowledge of some things as a function of age is a delta function.

Offline

**noelevans****Member**- Registered: 2012-07-20
- Posts: 236

Three digit numbers with two 3's and one 1 or with two 1's and one 3. Only one of them is NOT a

prime.

LaTex is like painting on many strips of paper and then stacking them to see what picture they make.

Offline

**noelevans****Member**- Registered: 2012-07-20
- Posts: 236

2 --- the only number for which any positive integer can be written as a sum of non-negative powers of that number alone using each power of the number no more than once.

LaTex is like painting on many strips of paper and then stacking them to see what picture they make.

Offline

**mathgogocart****Member**- Registered: 2012-04-29
- Posts: 1,472

101-1-1=0-the first sensible number

Hey.

Offline

**mathaholic****Member**- From: Earth
- Registered: 2012-11-29
- Posts: 3,025

My answer

*Last edited by julianthemath (2012-12-13 18:05:18)*

Mathaholic | 17th most active poster | 681st most recent person to join MIFF | Person | rrr's classmate

Offline

**mathgogocart****Member**- Registered: 2012-04-29
- Posts: 1,472

111 3 digits repeated trpile

Hey.

Offline

**mathaholic****Member**- From: Earth
- Registered: 2012-11-29
- Posts: 3,025

Mathgogocart, 111 is not prime. It is divisible by 1, 3, 37, 111 (ay be incomplete).

Offline

**mathgogocart****Member**- Registered: 2012-04-29
- Posts: 1,472

2

Hey.

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 100,263

I think you already picked 2.

101 - a room with a special meaning.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.** **Thinking is cheating.**

Offline

**mathaholic****Member**- From: Earth
- Registered: 2012-11-29
- Posts: 3,025

bobbym wrote:

101 - a room with a special meaning.

What is the special meaning?

17-the sum of the first four primes.

Offline

**scientia****Member**- Registered: 2009-11-13
- Posts: 224

According to the Old Testament, **31** kings were defeated by Joshua after the children of Israel had crossed the river Jordan (Joshua 12:924).

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 100,263

1111111111111111111

The second repunit that is prime.

julianthemath wrote:

What is the special meaning?

You are a little young yet but some day you will read 1984.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.** **Thinking is cheating.**

Offline

**mathaholic****Member**- From: Earth
- Registered: 2012-11-29
- Posts: 3,025

Oh, okay.

113-the 30th prime.

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 100,263

11111111111111111111111 the 3rd repunit that is a prime.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.** **Thinking is cheating.**

Offline