21316831 has 2 divisors, whose sum is σ = 21316832. Its totient is φ = 21316830.

The previous prime is 21316819. The next prime is 21316849. The reversal of 21316831 is 13861312.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21316831 - 2⁹ = 21316319 is a prime.

It is a super-2 number, since 2×21316831² = 908814567765122, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21316796 and 21316805.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21316891) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10658415 + 10658416.

It is an arithmetic number, because the mean of its divisors is an integer number (10658416).

Almost surely, 2^21316831 is an apocalyptic number.

21316831 is a deficient number, since it is larger than the sum of its proper divisors (1).

21316831 is an equidigital number, since it uses as much as digits as its factorization.

21316831 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 864, while the sum is 25.

The square root of 21316831 is about 4617.0153779254. The cubic root of 21316831 is about 277.2729782998.

The spelling of 21316831 in words is "twenty-one million, three hundred sixteen thousand, eight hundred thirty-one".