251755561 has 2 divisors, whose sum is σ = 251755562. Its totient is φ = 251755560.

The previous prime is 251755531. The next prime is 251755577. The reversal of 251755561 is 165557152.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 126427536 + 125328025 = 11244^2 + 11195^2 .

It is a cyclic number.

It is not a de Polignac number, because 251755561 - 2²⁵ = 218201129 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 251755561.

It is not a weakly prime, because it can be changed into another prime (251755531) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 125877780 + 125877781.

It is an arithmetic number, because the mean of its divisors is an integer number (125877781).

Almost surely, 2^251755561 is an apocalyptic number.

It is an amenable number.

251755561 is a deficient number, since it is larger than the sum of its proper divisors (1).

251755561 is an equidigital number, since it uses as much as digits as its factorization.

251755561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 52500, while the sum is 37.

The square root of 251755561 is about 15866.8068936381. The cubic root of 251755561 is about 631.4316655717.

The spelling of 251755561 in words is "two hundred fifty-one million, seven hundred fifty-five thousand, five hundred sixty-one".