• 556 can be written using four 4's:
It is a happy number.
It is a magnanimous number.
It is a plaindrome in base 9, base 10, base 11, base 13 and base 16.
It is a nialpdrome in base 5.
556 is an untouchable number, because it is not equal to the sum of proper divisors of any number.
It is an amenable number.
556 is a wasteful number, since it uses less digits than its factorization.
556 is an evil number, because the sum of its binary digits is even.
The square root of 556 is about 23.5796522451. The cubic root of 556 is about 8.2228985186. Note that the first 3 decimals are identical.
Subtracting from 556 its product of digits (150), we obtain a triangular number (406 = T28).
Subtracting 556 from its reverse (655), we obtain a palindrome (99).