### About the Number 400 (four hundred)

While creating a collection of square numbers, MathBabbler was surprised to learn he didn't have a nBAB for the number `400`.

```   MathBabbler Number Analyst (MBNA) output:
=========================================
400 is a natural, whole, integer
400 is even
400 proper divisors are: 1,2,4,5,8,10,16,20,25,40,50,80,100,200,
400 is abundant (sum of divisors is 561)
400 is unhappy
400 is a Harshad number
400 is not prime
400 has the prime factors: 2*2*2*2*5*5
400 sum prime factors: 18
400 in octal is 0620
400 in hexadecimal is 0x190
400 in binary is 110010000 (is odious)
400 is a square number
sqrt(400) = 20
ln(400) = 5.99146
log(400) = 2.60206
400 is 20^2
400 reciprocal is .00250000000000000000000000000000
400! is 6.40345e+868
400 is 127.324 Pi years
400 is 20 scoreyears
400 written as a Roman numeral is CD
```
##### Update::2009.08.25

On 25 August 2009, Google morphed its logo to celebrate the 400th anniversary of Italian astronomer Galilei Galileo's demonstration of his telescope.

Between the time this nBAB was created (10 April 2009) and the time of this update, the basen program was written and it produced the following output.

`400` in base-16 is 1024 (i.e. 2^10).

`400` in base-15 is square number 900.

`400` in base-8 is 256 (i.e. 2^8).

`400` in base-7 is square number 196 (i.e. 14^2).

`400` in base-6 is square number 144 (i.e. 12^2).

`400` in base-5 is square number 100 (i.e. 10^2).

##### Update::2009.12.15

MathBabbler posted his `400`th tweet on 15 December 2009. MathBabbler has been tweeting at a rate of almost 2.1 tweets per day since posting his first tweet on 8 June 2009.

Between the date this nBAB was last updated (25 August 2009) and the date of this update, the logs program was written and it reported that `log9(400)` `(2.72683)` truncated to two-decimal digits equals e `(2.7182818284590)` rounded to the nearest hundredth.

MathBABs.us::Number Basic Arithmetic Bits (BABs) Homepage

Creator: Gerald Thurman [gthurman@gmail.com]
Created: 10 April 2009 (posted 13 May 2009) 