21298972636561 has 27 divisors (see below), whose sum is σ = 22916105373819. Its totient is φ = 19792937868912.

The previous prime is 21298972636549. The next prime is 21298972636573. The reversal of 21298972636561 is 16563627989212.

The square root of 21298972636561 is 4615081.

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

It is an interprime number because it is at equal distance from previous prime (21298972636549) and next prime (21298972636573).

It can be written as a sum of positive squares in only one way, i.e., 15354367956225 + 5944604680336 = 3918465^2 + 2438156^2 .

It is not a de Polignac number, because 21298972636561 - 2²¹ = 21298970539409 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21298972639561) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 4647384276 + ... + 4647388858.

Almost surely, 2^{21298972636561} is an apocalyptic number.

21298972636561 is the 4615081-st square number.

21298972636561 is the 2307541-st centered octagonal number.

It is an amenable number.

21298972636561 is a deficient number, since it is larger than the sum of its proper divisors (1617132737258).

21298972636561 is an frugal number, since it uses more digits than its factorization.

21298972636561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9310 (or 4655 counting only the distinct ones).

The product of its digits is 117573120, while the sum is 67.

The spelling of 21298972636561 in words is "twenty-one trillion, two hundred ninety-eight billion, nine hundred seventy-two million, six hundred thirty-six thousand, five hundred sixty-one".