### About the Number 70 (seventy)

MathBabbler posted a nBAB for the number 31 and he noticed he didn't have a nBAB for the number 30. He did have nBABs for 10, 20, 40, 50, 60, 90, 100, 200, 500, 1500, 1600, 1700, 1800, 1900, 2000, 2100 and 8100 (all multiples of 10). MathBabbler opted to create a nBAB for the number 80 because his mom turned 80 in 2009. After posting the nBAB for the number 80 he decided to go ahead and create a nBAB for the number 30. Given he had nBABs for 10, 20, 30, 40, 50, 60, 80, 90, 100, he proceeded to create this nBAB about the number `70`.

```   MathBabbler Number Analyst (MBNA) output:
=========================================
70 is a natural, whole, integer
70 is even
70 proper divisors are: 1,2,5,7,10,14,35,
70 is abundant (sum of divisors is 74)
70 is happy
70 is a Harshad number
70 is not prime
70 is undulating
70 has the prime factors: 2*5*7
70 in octal is 0106
70 in hexadecimal is 0x46
70 in binary is 1000110 (is odious)
70 nearest square numbers: -6...11 (64...81 )
sqrt(70) = 8.3666
ln(70) = 4.2485
log(70) = 1.8451
70 reciprocal is .01428571428571428571428571428571
70! is 1.19786e+100
70 is 22.2817 Pi years
70 is 3 score and 10 years
70 written as a Roman numeral is LXX
```

`[Wikipedia]` `70` is the smallest weird number. Reading this prompted MathBabbler to ask: What makes a number weird?

```   "A weird number is a natural number that is abundant but
not semiperfect. In other words, the sum of the proper
divisors (divisors including 1 but not itself) of the
number is greater than the number, but no subset of
those divisors sums to the number itself."
[source: Wikipedia]
```

OEIS.org::id:A006037

The following are the first ten weird numbers.

```   70, 836, 4030, 5830, 7192, 7912, 9272, 10430, 10570, 10792
```

`70` is the first weird number to have a nBAB created for it.

##### Update::2011.05.24

Bob Dylan turned `70` years young on 24 May 2011.

The MBNA had changed since this nBAB was created on 27 February 2009.

```   70 is sphenic (has 3 unique prime factors)
70 is pentagonal
7011 is repdigit number 77
```

Creator: Gerald Thurman [gthurman@gmail.com]
Created: 27 February 2009 