Monday, November 15, 2010

70

70 = 2 x 5 x 7.

The sum of its divisors, including 70 itself, is a square (144): 1 + 2 + 5 + 7 + 10 + 14 + 35 + 70 = 144 = 122.

70 has a unique representation as a sum of three squares: 70 = 32 + 52 + 62.

70 is the 5th pentatope number.

70 is 77 in base 9.

Three score years and ten (70) is traditionally considered the natural human life span.

Source: The Penguin Dictionary of Curious and Interesting Numbers, rev. ed., by David Wells.

1 comment:

Amy W. said...

The sum of the proper factors of 70is more than 70, yet there is not a subset of the proper factors that adds up to 70. This is a "Weird number". 70 is the smallest weird number.