20556 has 18 divisors (see below), whose sum is σ = 52052. Its totient is φ = 6840.

The previous prime is 20551. The next prime is 20563. The reversal of 20556 is 65502.

20556 is nontrivially palindromic in base 5.

It is a tau number, because it is divible by the number of its divisors (18).

It is a hoax number, since the sum of its digits (18) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a nialpdrome in base 12.

It is not an unprimeable number, because it can be changed into a prime (20551) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 250 + ... + 321.

2²⁰⁵⁵⁶ is an apocalyptic number.

It is an amenable number.

20556 is an abundant number, since it is smaller than the sum of its proper divisors (31496).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

20556 is a wasteful number, since it uses less digits than its factorization.

20556 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 581 (or 576 counting only the distinct ones).

The product of its (nonzero) digits is 300, while the sum is 18.

The square root of 20556 is about 143.3736377442. The cubic root of 20556 is about 27.3934166434.

It can be divided in two parts, 20 and 556, that added together give a square (576 = 24²).

The spelling of 20556 in words is "twenty thousand, five hundred fifty-six".