21256265479681 has 4 divisors (see below), whose sum is σ = 21830759141332. Its totient is φ = 20681771818032.

The previous prime is 21256265479679. The next prime is 21256265479703. The reversal of 21256265479681 is 18697456265212.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 10759443065281 + 10496822414400 = 3280159^2 + 3239880^2 .

It is a cyclic number.

It is not a de Polignac number, because 21256265479681 - 2¹ = 21256265479679 is a prime.

It is a super-2 number, since 2×21256265479681² (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 (21256265479181) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 287246830770 + ... + 287246830843.

It is an arithmetic number, because the mean of its divisors is an integer number (5457689785333).

Almost surely, 2^{21256265479681} is an apocalyptic number.

It is an amenable number.

21256265479681 is a deficient number, since it is larger than the sum of its proper divisors (574493661651).

21256265479681 is an equidigital number, since it uses as much as digits as its factorization.

21256265479681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 574493661650.

The product of its digits is 87091200, while the sum is 64.

The spelling of 21256265479681 in words is "twenty-one trillion, two hundred fifty-six billion, two hundred sixty-five million, four hundred seventy-nine thousand, six hundred eighty-one".