21644244581 has 2 divisors, whose sum is σ = 21644244582. Its totient is φ = 21644244580.

The previous prime is 21644244563. The next prime is 21644244613. The reversal of 21644244581 is 18544244612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15471628225 + 6172616356 = 124385^2 + 78566^2 .

It is a cyclic number.

It is not a de Polignac number, because 21644244581 - 2²² = 21640050277 is a prime.

It is a super-2 number, since 2×21644244581² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21644244521) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10822122290 + 10822122291.

It is an arithmetic number, because the mean of its divisors is an integer number (10822122291).

Almost surely, 2^21644244581 is an apocalyptic number.

It is an amenable number.

21644244581 is a deficient number, since it is larger than the sum of its proper divisors (1).

21644244581 is an equidigital number, since it uses as much as digits as its factorization.

21644244581 is an evil number, because the sum of its binary digits is even.

The product of its digits is 245760, while the sum is 41.

The spelling of 21644244581 in words is "twenty-one billion, six hundred forty-four million, two hundred forty-four thousand, five hundred eighty-one".