21315031 has 2 divisors, whose sum is σ = 21315032. Its totient is φ = 21315030.

The previous prime is 21315023. The next prime is 21315037. The reversal of 21315031 is 13051312.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21315031 - 2³ = 21315023 is a prime.

It is a super-2 number, since 2×21315031² = 908661093061922, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21314996 and 21315014.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21315037) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10657515 + 10657516.

It is an arithmetic number, because the mean of its divisors is an integer number (10657516).

Almost surely, 2^21315031 is an apocalyptic number.

21315031 is a deficient number, since it is larger than the sum of its proper divisors (1).

21315031 is an equidigital number, since it uses as much as digits as its factorization.

21315031 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 90, while the sum is 16.

The square root of 21315031 is about 4616.8204426856. The cubic root of 21315031 is about 277.2651737406.

Adding to 21315031 its reverse (13051312), we get a palindrome (34366343).

The spelling of 21315031 in words is "twenty-one million, three hundred fifteen thousand, thirty-one".