21637868641 has 2 divisors, whose sum is σ = 21637868642. Its totient is φ = 21637868640.

The previous prime is 21637868579. The next prime is 21637868647. The reversal of 21637868641 is 14686873612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16832467600 + 4805401041 = 129740^2 + 69321^2 .

It is a cyclic number.

It is not a de Polignac number, because 21637868641 - 2¹³ = 21637860449 is a prime.

It is not a weakly prime, because it can be changed into another prime (21637868647) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10818934320 + 10818934321.

It is an arithmetic number, because the mean of its divisors is an integer number (10818934321).

Almost surely, 2^21637868641 is an apocalyptic number.

It is an amenable number.

21637868641 is a deficient number, since it is larger than the sum of its proper divisors (1).

21637868641 is an equidigital number, since it uses as much as digits as its factorization.

21637868641 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2322432, while the sum is 52.

The spelling of 21637868641 in words is "twenty-one billion, six hundred thirty-seven million, eight hundred sixty-eight thousand, six hundred forty-one".