251717644561 has 2 divisors, whose sum is σ = 251717644562. Its totient is φ = 251717644560.

The previous prime is 251717644559. The next prime is 251717644631. The reversal of 251717644561 is 165446717152.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 217500044161 + 34217600400 = 466369^2 + 184980^2 .

It is a cyclic number.

It is not a de Polignac number, because 251717644561 - 2¹ = 251717644559 is a prime.

Together with 251717644559, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (251717644531) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 125858822280 + 125858822281.

It is an arithmetic number, because the mean of its divisors is an integer number (125858822281).

Almost surely, 2^251717644561 is an apocalyptic number.

It is an amenable number.

251717644561 is a deficient number, since it is larger than the sum of its proper divisors (1).

251717644561 is an equidigital number, since it uses as much as digits as its factorization.

251717644561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1411200, while the sum is 49.

The spelling of 251717644561 in words is "two hundred fifty-one billion, seven hundred seventeen million, six hundred forty-four thousand, five hundred sixty-one".