561

561 is a natural number that succeeds 560 and comes before 562.

Properties
561 is an interesting number primarily for the reason that $$561^2-561^1-561^0=314159$$. The resulting number 314159 contains the first 6|six decimal digits of pi.

561 has 3, 11, and 17 as it's prime factors, incidentally the sum of those prime factors is 31, which happens to be the first 2|two decimal digits of pi.

Origin
561 was noted for having this property by Edwin Shade about two years ago.