21715931 has 2 divisors, whose sum is σ = 21715932. Its totient is φ = 21715930.

The previous prime is 21715921. The next prime is 21715951. The reversal of 21715931 is 13951712.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21715931 - 2¹⁰ = 21714907 is a prime.

It is a super-2 number, since 2×21715931² = 943163318393522, which contains 22 as substring.

It is a Sophie Germain prime.

It is a junction number, because it is equal to n+sod(n) for n = 21715894 and 21715903.

It is not a weakly prime, because it can be changed into another prime (21715921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10857965 + 10857966.

It is an arithmetic number, because the mean of its divisors is an integer number (10857966).

Almost surely, 2^21715931 is an apocalyptic number.

21715931 is a deficient number, since it is larger than the sum of its proper divisors (1).

21715931 is an equidigital number, since it uses as much as digits as its factorization.

21715931 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1890, while the sum is 29.

The square root of 21715931 is about 4660.0355148861. The cubic root of 21715931 is about 278.9926857535.

The spelling of 21715931 in words is "twenty-one million, seven hundred fifteen thousand, nine hundred thirty-one".