21660537 has 16 divisors (see below), whose sum is σ = 29954048. Its totient is φ = 13908240.

The previous prime is 21660523. The next prime is 21660559. The reversal of 21660537 is 73506612.

It is not a de Polignac number, because 21660537 - 2⁴ = 21660521 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21660137) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 25908 + ... + 26730.

It is an arithmetic number, because the mean of its divisors is an integer number (1872128).

Almost surely, 2^21660537 is an apocalyptic number.

It is an amenable number.

21660537 is a deficient number, since it is larger than the sum of its proper divisors (8293511).

21660537 is a wasteful number, since it uses less digits than its factorization.

21660537 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1140.

The product of its (nonzero) digits is 7560, while the sum is 30.

The square root of 21660537 is about 4654.0882028599. The cubic root of 21660537 is about 278.7552612841.

The spelling of 21660537 in words is "twenty-one million, six hundred sixty thousand, five hundred thirty-seven".