256642653221 has 4 divisors (see below), whose sum is σ = 267801029472. Its totient is φ = 245484276972.

The previous prime is 256642653209. The next prime is 256642653233. The reversal of 256642653221 is 122356246652.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is an interprime number because it is at equal distance from previous prime (256642653209) and next prime (256642653233).

It is a cyclic number.

It is not a de Polignac number, because 256642653221 - 2²² = 256638458917 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (256642653251) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5579188091 + ... + 5579188136.

It is an arithmetic number, because the mean of its divisors is an integer number (66950257368).

Almost surely, 2^256642653221 is an apocalyptic number.

It is an amenable number.

256642653221 is a deficient number, since it is larger than the sum of its proper divisors (11158376251).

256642653221 is a wasteful number, since it uses less digits than its factorization.

256642653221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11158376250.

The product of its digits is 1036800, while the sum is 44.

Adding to 256642653221 its reverse (122356246652), we get a palindrome (378998899873).

The spelling of 256642653221 in words is "two hundred fifty-six billion, six hundred forty-two million, six hundred fifty-three thousand, two hundred twenty-one".