21604551 has 8 divisors (see below), whose sum is σ = 29735424. Its totient is φ = 13938360.

The previous prime is 21604529. The next prime is 21604579. The reversal of 21604551 is 15540612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21604551 - 2⁶ = 21604487 is a prime.

It is a Smith number, since the sum of its digits (24) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21604151) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 116061 + ... + 116246.

It is an arithmetic number, because the mean of its divisors is an integer number (3716928).

Almost surely, 2^21604551 is an apocalyptic number.

21604551 is a deficient number, since it is larger than the sum of its proper divisors (8130873).

21604551 is a wasteful number, since it uses less digits than its factorization.

21604551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 232341.

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

The square root of 21604551 is about 4648.0695993068. The cubic root of 21604551 is about 278.5148877829.

It can be divided in two parts, 21604 and 551, that added together give a triangular number (22155 = T₂₁₀).

The spelling of 21604551 in words is "twenty-one million, six hundred four thousand, five hundred fifty-one".