21644531 has 2 divisors, whose sum is σ = 21644532. Its totient is φ = 21644530.

The previous prime is 21644509. The next prime is 21644543. The reversal of 21644531 is 13544612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21644531 - 2¹⁰ = 21643507 is a prime.

It is a super-2 number, since 2×21644531² = 936971444419922, which contains 22 as substring.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21644531.

It is not a weakly prime, because it can be changed into another prime (21644731) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10822265 + 10822266.

It is an arithmetic number, because the mean of its divisors is an integer number (10822266).

Almost surely, 2^21644531 is an apocalyptic number.

21644531 is a deficient number, since it is larger than the sum of its proper divisors (1).

21644531 is an equidigital number, since it uses as much as digits as its factorization.

21644531 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2880, while the sum is 26.

The square root of 21644531 is about 4652.3683216186. The cubic root of 21644531 is about 278.6865825287.

The spelling of 21644531 in words is "twenty-one million, six hundred forty-four thousand, five hundred thirty-one".