21646636441 has 2 divisors, whose sum is σ = 21646636442. Its totient is φ = 21646636440.

The previous prime is 21646636423. The next prime is 21646636471. The reversal of 21646636441 is 14463664612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16461916416 + 5184720025 = 128304^2 + 72005^2 .

It is a cyclic number.

It is not a de Polignac number, because 21646636441 - 2⁷ = 21646636313 is a prime.

It is not a weakly prime, because it can be changed into another prime (21646636471) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10823318220 + 10823318221.

It is an arithmetic number, because the mean of its divisors is an integer number (10823318221).

Almost surely, 2^21646636441 is an apocalyptic number.

It is an amenable number.

21646636441 is a deficient number, since it is larger than the sum of its proper divisors (1).

21646636441 is an equidigital number, since it uses as much as digits as its factorization.

21646636441 is an evil number, because the sum of its binary digits is even.

The product of its digits is 497664, while the sum is 43.

The spelling of 21646636441 in words is "twenty-one billion, six hundred forty-six million, six hundred thirty-six thousand, four hundred forty-one".