21253931 has 2 divisors, whose sum is σ = 21253932. Its totient is φ = 21253930.

The previous prime is 21253919. The next prime is 21253937. The reversal of 21253931 is 13935212.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21253931 is a prime.

It is a super-2 number, since 2×21253931² = 903459165905522, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21253931.

It is not a weakly prime, because it can be changed into another prime (21253937) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10626965 + 10626966.

It is an arithmetic number, because the mean of its divisors is an integer number (10626966).

Almost surely, 2^21253931 is an apocalyptic number.

21253931 is a deficient number, since it is larger than the sum of its proper divisors (1).

21253931 is an equidigital number, since it uses as much as digits as its factorization.

21253931 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1620, while the sum is 26.

The square root of 21253931 is about 4610.1985857444. The cubic root of 21253931 is about 276.9999913114. Note that the first 5 decimals are identical.

The spelling of 21253931 in words is "twenty-one million, two hundred fifty-three thousand, nine hundred thirty-one".