## What is Your Favorite Number?

*March 21, 2011 at 4:24 am* *
8 comments *

The WordPress Post-A-Week Challenge sends me a daily topic idea to consider for blog posts. Often, the prompts are not appropriate for a math jokes blog. For instance, some recent prompts have been:

- Grab the nearest book (or website) to you right now. Jump to paragraph 3, second sentence. Write it in a post.
- How do you find your muse?
- If you could bring one fictional character to life for a day, who would you choose?

But today’s prompt landed in my wheelhouse:

What is your favorite number, and why?

When Art Benjamin appeared on the Colbert Report, he said that 2,520 was his favorite number when he was a kid. When Stephen Colbert asked him why, he replied, “It was the smallest number that was divisible by all the numbers from 1 through 10.”

Tonight, I asked my twin sons Alex and Eli what their favorite numbers are.

Eli: 5, 15, 55, because my favorite number is really 5, but 15 and 55 are triangular numbers that have 5′s in them.

Alex: 21, because my favorite numbers used to be 1 and 2, and because it’s the number of cards you deal when we play Uno (3 players, 7 cards each).

My favorite number is 153, for lots of reasons:

- It is the smallest non-trivial Armstrong (or narcissistic) number — that is, it is an
*n*‑digit number that is equal to the sum of the*n*th powers of its digits: 1^{3}+ 5^{3}+ 3^{3}= 153. - Its prime factors are 3 and 17, and my birthday is 3/17.
- It is a triangular number. (Consequently, it’s the sum of 1 + 2 + 3 + … + 17.) As 351 is also a triangular number, 153 is also a reversible triangular number.
- It is the sum of the first five factorials: 1! + 2! + 3! + 4! + 5! = 153.
- The sum of its digits is 9, and the sum of its proper divisors is 9
^{2}. - It is one of only six known truncated triangular numbers, which means that 1, 15 and 153 are all triangular numbers.

Mathematician John Baez claims that his favorite numbers are 5, 8, and 24.

Got a favorite number? Share it, as well as the reason it’s your favorite, in the comments.

Entry filed under: Uncategorized. Tags: factor, favorite, number, postaweek2011, triangular, WordPress.

1.Jims | March 21, 2011 at 6:58 amZero• It is the additive identity (n+0=n when ‘n’ is any number).

• 0 is not positive or negative.

• The only number in base 1 is 0.

• Like all Popular numbers, 0 has it’s own meme (Dividing by Zero causes amazing things in peoples imaginations). Note: the set of Popular numbers is undefined.

• 0 is a Whole number but not a Natural number, and that’s the only difference between them.

• 0 and the {} … need I say more?

I was going to have zero explanations, but that would’ve been pointless.

2.xander | March 21, 2011 at 11:21 amI know that it is terribly cliché, but I rather like

e(Euler’s number). It pops up all over the place—often in unexpected ways. Exponential functions behave nicely with respected to differentiation, and the exponential distribution is the only continuous memoryless distribution.egreat.3.Bon Crowder | March 21, 2011 at 1:37 pmI like 4. Just simple. And square. And the first non-unit square whole number.

And nobody seems to have 4 as their fav. So it is less likely to be hogged by others.

4.Veky | March 22, 2011 at 2:47 amWow, and I thought I was unique in liking 4 and 153. :-)

5.mixedmath | March 22, 2011 at 5:59 am1001.

It’s the product of the first three ‘non-obvious’ primes, 7,11,13. These primes are the first whose divisibility rules take a little thought, and it turns out that 1001 provides the key as it’s only 1 away from 10^3.

6.zach | March 22, 2011 at 8:57 pmmy favorite number 705:

705 is the product of 3, 5, and 47 which are the unique prime numbers in the prime decomposition of the numbers 15 May 47 (5/15/47) my birthday.

The 705th Strong Number (Greek) is “To Number” “ἀριθμέω” (transliteration – “arithmeō”)

705 Is: The 4th 73-Gonal Number (72-gonal Numbers 1, 72, 213, 424, 705, 1038, 1477, 1968, 2529..)

705 Is: The 3rd 236-Gonal Number (236-gonal Numbers 1, 236, 705, 1408, 2345..)

705 Is: The First Lucas Pseudoprime

7.Bryan McDonald | March 28, 2011 at 10:33 am“73 is the 21st prime number. Its mirror 37 is the 12th and its mirror 21 is the product of multiplying, hold on to your hats, 7 and 3. In binary, 73 is a palindrome, 1, 0, 0 1, 0, 0, 1 which backwards is 1, 0, 0 1, 0, 0, 1″

Sheldon Cooper

Big Bang Theory

8.Chloe | May 5, 2011 at 8:46 pm36. The reason? It is the smallest number that is both a triangle and a square, and it’s square root is 6, the first mathematically perfect number. In fact, one could argue it is the most perfect, because it’s factors added AND multiplied both equal it. I am proud to say that I, a 14 year-old, figured this out on my own :D