21640531 has 8 divisors (see below), whose sum is σ = 23961024. Its totient is φ = 19378920.

The previous prime is 21640529. The next prime is 21640537. The reversal of 21640531 is 13504612.

21640531 = T₇₇₀ + T₇₇₁ + ... + T₈₃₆.

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

It is not a de Polignac number, because 21640531 - 2¹ = 21640529 is a prime.

It is a super-2 number, since 2×21640531² = 936625163923922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21640537) 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, 13945 + ... + 15418.

It is an arithmetic number, because the mean of its divisors is an integer number (2995128).

Almost surely, 2^21640531 is an apocalyptic number.

21640531 is a deficient number, since it is larger than the sum of its proper divisors (2320493).

21640531 is a wasteful number, since it uses less digits than its factorization.

21640531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 29441.

The product of its (nonzero) digits is 720, while the sum is 22.

The square root of 21640531 is about 4651.9384131779. The cubic root of 21640531 is about 278.6694139884.

The spelling of 21640531 in words is "twenty-one million, six hundred forty thousand, five hundred thirty-one".