21812731 has 2 divisors, whose sum is σ = 21812732. Its totient is φ = 21812730.

The previous prime is 21812723. The next prime is 21812737. The reversal of 21812731 is 13721812.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21812731 - 2³ = 21812723 is a prime.

It is a super-2 number, since 2×21812731² = 951590467356722, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21812696 and 21812705.

It is not a weakly prime, because it can be changed into another prime (21812737) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10906365 + 10906366.

It is an arithmetic number, because the mean of its divisors is an integer number (10906366).

Almost surely, 2^21812731 is an apocalyptic number.

21812731 is a deficient number, since it is larger than the sum of its proper divisors (1).

21812731 is an equidigital number, since it uses as much as digits as its factorization.

21812731 is an evil number, because the sum of its binary digits is even.

The product of its digits is 672, while the sum is 25.

The square root of 21812731 is about 4670.4101532949. The cubic root of 21812731 is about 279.4066132583.

The spelling of 21812731 in words is "twenty-one million, eight hundred twelve thousand, seven hundred thirty-one".