21540731 has 2 divisors, whose sum is σ = 21540732. Its totient is φ = 21540730.

The previous prime is 21540709. The next prime is 21540763. The reversal of 21540731 is 13704512.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21540731 is a prime.

It is a super-2 number, since 2×21540731² = 928006184028722, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21540697 and 21540706.

It is not a weakly prime, because it can be changed into another prime (21540791) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10770365 + 10770366.

It is an arithmetic number, because the mean of its divisors is an integer number (10770366).

Almost surely, 2^21540731 is an apocalyptic number.

21540731 is a deficient number, since it is larger than the sum of its proper divisors (1).

21540731 is an equidigital number, since it uses as much as digits as its factorization.

21540731 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 840, while the sum is 23.

The square root of 21540731 is about 4641.1993062139. The cubic root of 21540731 is about 278.2403723002.

The spelling of 21540731 in words is "twenty-one million, five hundred forty thousand, seven hundred thirty-one".