21644243237 has 2 divisors, whose sum is σ = 21644243238. Its totient is φ = 21644243236.

The previous prime is 21644243233. The next prime is 21644243329. The reversal of 21644243237 is 73234244612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15087454561 + 6556788676 = 122831^2 + 80974^2 .

It is a cyclic number.

It is not a de Polignac number, because 21644243237 - 2² = 21644243233 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21644243237.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21644243233) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10822121618 + 10822121619.

It is an arithmetic number, because the mean of its divisors is an integer number (10822121619).

Almost surely, 2^21644243237 is an apocalyptic number.

It is an amenable number.

21644243237 is a deficient number, since it is larger than the sum of its proper divisors (1).

21644243237 is an equidigital number, since it uses as much as digits as its factorization.

21644243237 is an evil number, because the sum of its binary digits is even.

The product of its digits is 193536, while the sum is 38.

Adding to 21644243237 its reverse (73234244612), we get a palindrome (94878487849).

The spelling of 21644243237 in words is "twenty-one billion, six hundred forty-four million, two hundred forty-three thousand, two hundred thirty-seven".