21287564 has 6 divisors (see below), whose sum is σ = 37253244. Its totient is φ = 10643780.

The previous prime is 21287551. The next prime is 21287633. The reversal of 21287564 is 46578212.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2660942 + ... + 2660949.

It is an arithmetic number, because the mean of its divisors is an integer number (6208874).

Almost surely, 2^21287564 is an apocalyptic number.

It is an amenable number.

21287564 is a deficient number, since it is larger than the sum of its proper divisors (15965680).

21287564 is a wasteful number, since it uses less digits than its factorization.

21287564 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5321895 (or 5321893 counting only the distinct ones).

The product of its digits is 26880, while the sum is 35.

The square root of 21287564 is about 4613.8448175031. The cubic root of 21287564 is about 277.1460259571.

The spelling of 21287564 in words is "twenty-one million, two hundred eighty-seven thousand, five hundred sixty-four".