21638842641 has 18 divisors (see below), whose sum is σ = 33845371638. Its totient is φ = 13316209920.

The previous prime is 21638842637. The next prime is 21638842651. The reversal of 21638842641 is 14624883612.

21638842641 is a `hidden beast` number, since 2 + 1 + 6 + 388 + 4 + 264 + 1 = 666.

It can be written as a sum of positive squares in 3 ways, for example, as 1481942016 + 20156900625 = 38496^2 + 141975^2 .

It is not a de Polignac number, because 21638842641 - 2² = 21638842637 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21638842651) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 7111840 + ... + 7114881.

Almost surely, 2^21638842641 is an apocalyptic number.

It is an amenable number.

21638842641 is a deficient number, since it is larger than the sum of its proper divisors (12206528997).

21638842641 is a wasteful number, since it uses less digits than its factorization.

21638842641 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14226753 (or 14226737 counting only the distinct ones).

The product of its digits is 442368, while the sum is 45.

The spelling of 21638842641 in words is "twenty-one billion, six hundred thirty-eight million, eight hundred forty-two thousand, six hundred forty-one".