21239731 has 2 divisors, whose sum is σ = 21239732. Its totient is φ = 21239730.

The previous prime is 21239717. The next prime is 21239753. The reversal of 21239731 is 13793212.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21239731 is a prime.

It is a super-2 number, since 2×21239731² = 902252345904722, 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 21239731.

It is not a weakly prime, because it can be changed into another prime (21239711) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10619865 + 10619866.

It is an arithmetic number, because the mean of its divisors is an integer number (10619866).

Almost surely, 2^21239731 is an apocalyptic number.

21239731 is a deficient number, since it is larger than the sum of its proper divisors (1).

21239731 is an equidigital number, since it uses as much as digits as its factorization.

21239731 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2268, while the sum is 28.

The square root of 21239731 is about 4608.6582646146. The cubic root of 21239731 is about 276.9382885894.

The spelling of 21239731 in words is "twenty-one million, two hundred thirty-nine thousand, seven hundred thirty-one".