21637968665569 has 3 divisors (see below), whose sum is σ = 21637973317233. Its totient is φ = 21637964013906.

The previous prime is 21637968665563. The next prime is 21637968665591. The reversal of 21637968665569 is 96556686973612.

The square root of 21637968665569 is 4651663.

It is a perfect power (a square), and thus also a powerful number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is not a de Polignac number, because 21637968665569 - 2⁹ = 21637968665057 is a prime.

It is a super-2 number, since 2×21637968665569² (a number of 27 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21637968665563) by changing a digit.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 2325832 + ... + 6977494.

It is an arithmetic number, because the mean of its divisors is an integer number (7212657772411).

Almost surely, 2^{21637968665569} is an apocalyptic number.

21637968665569 is the 4651663-rd square number.

21637968665569 is the 2325832-nd centered octagonal number.

It is an amenable number.

21637968665569 is a deficient number, since it is larger than the sum of its proper divisors (4651664).

21637968665569 is an frugal number, since it uses more digits than its factorization.

21637968665569 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9303326 (or 4651663 counting only the distinct ones).

The product of its digits is 5290790400, while the sum is 79.

The spelling of 21637968665569 in words is "twenty-one trillion, six hundred thirty-seven billion, nine hundred sixty-eight million, six hundred sixty-five thousand, five hundred sixty-nine".