21138731 has 2 divisors, whose sum is σ = 21138732. Its totient is φ = 21138730.

The previous prime is 21138727. The next prime is 21138737. The reversal of 21138731 is 13783112.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21138731 - 2² = 21138727 is a prime.

It is a super-2 number, since 2×21138731² = 893691896580722, 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 21138731.

It is not a weakly prime, because it can be changed into another prime (21138737) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10569365 + 10569366.

It is an arithmetic number, because the mean of its divisors is an integer number (10569366).

Almost surely, 2^21138731 is an apocalyptic number.

21138731 is a deficient number, since it is larger than the sum of its proper divisors (1).

21138731 is an equidigital number, since it uses as much as digits as its factorization.

21138731 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1008, while the sum is 26.

The square root of 21138731 is about 4597.6875709426. The cubic root of 21138731 is about 276.4986216818.

The spelling of 21138731 in words is "twenty-one million, one hundred thirty-eight thousand, seven hundred thirty-one".