256723837561 has 4 divisors (see below), whose sum is σ = 260932425124. Its totient is φ = 252515250000.

The previous prime is 256723837549. The next prime is 256723837583. The reversal of 256723837561 is 165738327652.

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 50285371536 + 206438466025 = 224244^2 + 454355^2 .

It is a cyclic number.

It is not a de Polignac number, because 256723837561 - 2¹⁷ = 256723706489 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (256723837511) 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, 2104293690 + ... + 2104293811.

It is an arithmetic number, because the mean of its divisors is an integer number (65233106281).

Almost surely, 2^256723837561 is an apocalyptic number.

It is an amenable number.

256723837561 is a deficient number, since it is larger than the sum of its proper divisors (4208587563).

256723837561 is an equidigital number, since it uses as much as digits as its factorization.

256723837561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4208587562.

The product of its digits is 12700800, while the sum is 55.

The spelling of 256723837561 in words is "two hundred fifty-six billion, seven hundred twenty-three million, eight hundred thirty-seven thousand, five hundred sixty-one".