256423135561 has 2 divisors, whose sum is σ = 256423135562. Its totient is φ = 256423135560.

The previous prime is 256423135531. The next prime is 256423135571. The reversal of 256423135561 is 165531324652.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 245402335161 + 11020800400 = 495381^2 + 104980^2 .

It is a cyclic number.

It is not a de Polignac number, because 256423135561 - 2⁹ = 256423135049 is a prime.

It is not a weakly prime, because it can be changed into another prime (256423135511) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 128211567780 + 128211567781.

It is an arithmetic number, because the mean of its divisors is an integer number (128211567781).

Almost surely, 2^256423135561 is an apocalyptic number.

It is an amenable number.

256423135561 is a deficient number, since it is larger than the sum of its proper divisors (1).

256423135561 is an equidigital number, since it uses as much as digits as its factorization.

256423135561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 648000, while the sum is 43.

The spelling of 256423135561 in words is "two hundred fifty-six billion, four hundred twenty-three million, one hundred thirty-five thousand, five hundred sixty-one".