21551604 has 12 divisors (see below), whose sum is σ = 50287104. Its totient is φ = 7183864.

The previous prime is 21551591. The next prime is 21551623. The reversal of 21551604 is 40615512.

It is a tau number, because it is divible by the number of its divisors (12).

It is a congruent number.

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 3 ways as a sum of consecutive naturals, for example, 897972 + ... + 897995.

It is an arithmetic number, because the mean of its divisors is an integer number (4190592).

Almost surely, 2^21551604 is an apocalyptic number.

It is an amenable number.

21551604 is an abundant number, since it is smaller than the sum of its proper divisors (28735500).

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

21551604 is a wasteful number, since it uses less digits than its factorization.

21551604 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1795974 (or 1795972 counting only the distinct ones).

The product of its (nonzero) digits is 1200, while the sum is 24.

The square root of 21551604 is about 4642.3705151571. The cubic root of 21551604 is about 278.2871797289.

It can be divided in two parts, 21551 and 604, that added together give a triangular number (22155 = T₂₁₀).

The spelling of 21551604 in words is "twenty-one million, five hundred fifty-one thousand, six hundred four".