21521616 has 20 divisors (see below), whose sum is σ = 55597632. Its totient is φ = 7173856.

The previous prime is 21521587. The next prime is 21521627. The reversal of 21521616 is 61612512.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 224136 + ... + 224231.

Almost surely, 2^21521616 is an apocalyptic number.

It is an amenable number.

21521616 is an abundant number, since it is smaller than the sum of its proper divisors (34076016).

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

21521616 is a wasteful number, since it uses less digits than its factorization.

21521616 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 448378 (or 448372 counting only the distinct ones).

The product of its digits is 720, while the sum is 24.

The square root of 21521616 is about 4639.1395753954. The cubic root of 21521616 is about 278.1580454949.

The spelling of 21521616 in words is "twenty-one million, five hundred twenty-one thousand, six hundred sixteen".