Friday, November 13, 2009

989

989 = 23 x 43.

989 is the smallest number so that it and its reverse are divisible by 43.

989 is 33131 in base 4 and 12424 in base 5.

989 is one of the integers generated by the following sieve: Keep first number, drop every second, keep first, drop every third, keep first, drop every fourth, and so on: 0, 1, 3, 5, 9, 11, 17, 21, 29, 33, . . . , 989, . . .

Halley's Comet was visible from Earth in the year 989.

Source: The On-Line Encyclopedia of Integer Sequences

1 comment:

Jacob said...

I was kind of disappointed with the smallest number whose reverse is also divisible by 989, so I thought I'd find the smallest number which wasn't a palindrome. Well, that turned out to be 9890, also a disappointment. However, the smallest number which neither is a palindrome now ends in a 0 such that both the number and its reverse are divisible by 43 is 13,803. I found this number to be much more satisfying.