Number Gossip

(Enter a number and I'll tell you everything you wanted to know about it but were afraid to ask.)

Unique Properties of 91

  • 91 is the first non-trivial composite: every smaller composite is either even, a familiar square, ends in 5, has a digit sum that is a multiple of 3, or is obviously divisible by 11
  • In cents of a U.S. dollar, 91 is the amount of money one has if one has one each of the coins of denominations less than a dollar (penny, nickel, dime, quarter and half dollar)

Common Properties of 91

Composite
Deficient
Happy
Odd
Odious
Square-free
Triangular