21660531 has 4 divisors (see below), whose sum is σ = 28880712. Its totient is φ = 14440352.

The previous prime is 21660523. The next prime is 21660559. The reversal of 21660531 is 13506612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21660531 - 2³ = 21660523 is a prime.

It is a super-2 number, since 2×21660531² = 938357206403922, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21660521) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3610086 + ... + 3610091.

It is an arithmetic number, because the mean of its divisors is an integer number (7220178).

Almost surely, 2^21660531 is an apocalyptic number.

21660531 is a deficient number, since it is larger than the sum of its proper divisors (7220181).

21660531 is an equidigital number, since it uses as much as digits as its factorization.

21660531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7220180.

The product of its (nonzero) digits is 1080, while the sum is 24.

The square root of 21660531 is about 4654.0875582653. The cubic root of 21660531 is about 278.7552355455.

The spelling of 21660531 in words is "twenty-one million, six hundred sixty thousand, five hundred thirty-one".