251065561 has 4 divisors (see below), whose sum is σ = 252982224. Its totient is φ = 249148900.

The previous prime is 251065543. The next prime is 251065567. The reversal of 251065561 is 165560152.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 251065561 - 2⁹ = 251065049 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (251065567) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 958135 + ... + 958396.

It is an arithmetic number, because the mean of its divisors is an integer number (63245556).

Almost surely, 2^251065561 is an apocalyptic number.

It is an amenable number.

251065561 is a deficient number, since it is larger than the sum of its proper divisors (1916663).

251065561 is a wasteful number, since it uses less digits than its factorization.

251065561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1916662.

The product of its (nonzero) digits is 9000, while the sum is 31.

The square root of 251065561 is about 15845.0484694746. The cubic root of 251065561 is about 630.8542715148.

The spelling of 251065561 in words is "two hundred fifty-one million, sixty-five thousand, five hundred sixty-one".