256621653036561 has 4 divisors (see below), whose sum is σ = 342162204048752. Its totient is φ = 171081102024372.

The previous prime is 256621653036557. The next prime is 256621653036571. The reversal of 256621653036561 is 165630356126652.

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 not a de Polignac number, because 256621653036561 - 2² = 256621653036557 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (256621653036571) 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, 42770275506091 + ... + 42770275506096.

It is an arithmetic number, because the mean of its divisors is an integer number (85540551012188).

Almost surely, 2^{256621653036561} is an apocalyptic number.

It is an amenable number.

256621653036561 is a deficient number, since it is larger than the sum of its proper divisors (85540551012191).

256621653036561 is an equidigital number, since it uses as much as digits as its factorization.

256621653036561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 85540551012190.

The product of its (nonzero) digits is 34992000, while the sum is 57.

The spelling of 256621653036561 in words is "two hundred fifty-six trillion, six hundred twenty-one billion, six hundred fifty-three million, thirty-six thousand, five hundred sixty-one".