21620556 has 72 divisors (see below), whose sum is σ = 58451120. Its totient is φ = 6718464.

The previous prime is 21620531. The next prime is 21620561. The reversal of 21620556 is 65502612.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 49716 + ... + 50148.

Almost surely, 2^21620556 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21620556, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29225560).

21620556 is an abundant number, since it is smaller than the sum of its proper divisors (36830564).

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

21620556 is a wasteful number, since it uses less digits than its factorization.

21620556 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 535 (or 530 counting only the distinct ones).

The product of its (nonzero) digits is 3600, while the sum is 27.

The square root of 21620556 is about 4649.7909630434. The cubic root of 21620556 is about 278.5836469141.

The spelling of 21620556 in words is "twenty-one million, six hundred twenty thousand, five hundred fifty-six".