251887561 has 2 divisors, whose sum is σ = 251887562. Its totient is φ = 251887560.

The previous prime is 251887543. The next prime is 251887607. The reversal of 251887561 is 165788152.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 175430025 + 76457536 = 13245^2 + 8744^2 .

It is a cyclic number.

It is not a de Polignac number, because 251887561 - 2⁵ = 251887529 is a prime.

It is not a weakly prime, because it can be changed into another prime (251887501) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 125943780 + 125943781.

It is an arithmetic number, because the mean of its divisors is an integer number (125943781).

Almost surely, 2^251887561 is an apocalyptic number.

It is an amenable number.

251887561 is a deficient number, since it is larger than the sum of its proper divisors (1).

251887561 is an equidigital number, since it uses as much as digits as its factorization.

251887561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 134400, while the sum is 43.

The square root of 251887561 is about 15870.9659756424. The cubic root of 251887561 is about 631.5420033092.

The spelling of 251887561 in words is "two hundred fifty-one million, eight hundred eighty-seven thousand, five hundred sixty-one".