21644668769 has 2 divisors, whose sum is σ = 21644668770. Its totient is φ = 21644668768.

The previous prime is 21644668697. The next prime is 21644668783. The reversal of 21644668769 is 96786644612.

Together with previous prime (21644668697) it forms an Ormiston pair, because they use the same digits, order apart.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18496000000 + 3148668769 = 136000^2 + 56113^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21644668769 is a prime.

It is a super-2 number, since 2×21644668769² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21644668789) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10822334384 + 10822334385.

It is an arithmetic number, because the mean of its divisors is an integer number (10822334385).

Almost surely, 2^21644668769 is an apocalyptic number.

It is an amenable number.

21644668769 is a deficient number, since it is larger than the sum of its proper divisors (1).

21644668769 is an equidigital number, since it uses as much as digits as its factorization.

21644668769 is an evil number, because the sum of its binary digits is even.

The product of its digits is 20901888, while the sum is 59.

The spelling of 21644668769 in words is "twenty-one billion, six hundred forty-four million, six hundred sixty-eight thousand, seven hundred sixty-nine".