256743620377721 has 4 divisors (see below), whose sum is σ = 259390461825012. Its totient is φ = 254096778930432.

The previous prime is 256743620377693. The next prime is 256743620377759. The reversal of 256743620377721 is 127773026347652.

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 52231769394025 + 204511850983696 = 7227155^2 + 14300764^2 .

It is a cyclic number.

It is not a de Polignac number, because 256743620377721 - 2¹⁴ = 256743620361337 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (256743620377771) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1323420723500 + ... + 1323420723693.

It is an arithmetic number, because the mean of its divisors is an integer number (64847615456253).

Almost surely, 2^{256743620377721} is an apocalyptic number.

It is an amenable number.

256743620377721 is a deficient number, since it is larger than the sum of its proper divisors (2646841447291).

256743620377721 is an equidigital number, since it uses as much as digits as its factorization.

256743620377721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2646841447290.

The product of its (nonzero) digits is 124467840, while the sum is 62.

The spelling of 256743620377721 in words is "two hundred fifty-six trillion, seven hundred forty-three billion, six hundred twenty million, three hundred seventy-seven thousand, seven hundred twenty-one".