21457931 has 8 divisors (see below), whose sum is σ = 23588928. Its totient is φ = 19357000.

The previous prime is 21457871. The next prime is 21457939. The reversal of 21457931 is 13975412.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21457931 is a prime.

It is a super-2 number, since 2×21457931² = 920885605601522, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21457939) 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, 6005 + ... + 8886.

It is an arithmetic number, because the mean of its divisors is an integer number (2948616).

Almost surely, 2^21457931 is an apocalyptic number.

21457931 is a deficient number, since it is larger than the sum of its proper divisors (2130997).

21457931 is a wasteful number, since it uses less digits than its factorization.

21457931 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15033.

The product of its digits is 7560, while the sum is 32.

The square root of 21457931 is about 4632.2706095391. The cubic root of 21457931 is about 277.8834069330.

The spelling of 21457931 in words is "twenty-one million, four hundred fifty-seven thousand, nine hundred thirty-one".