251215561 has 4 divisors (see below), whose sum is σ = 251290624. Its totient is φ = 251140500.

The previous prime is 251215553. The next prime is 251215567. The reversal of 251215561 is 165512152.

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 a cyclic number.

It is not a de Polignac number, because 251215561 - 2³ = 251215553 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (251215567) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 32265 + ... + 39286.

It is an arithmetic number, because the mean of its divisors is an integer number (62822656).

Almost surely, 2^251215561 is an apocalyptic number.

It is an amenable number.

251215561 is a deficient number, since it is larger than the sum of its proper divisors (75063).

251215561 is an equidigital number, since it uses as much as digits as its factorization.

251215561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 75062.

The product of its digits is 3000, while the sum is 28.

The square root of 251215561 is about 15849.7811025894. The cubic root of 251215561 is about 630.9798818684.

The spelling of 251215561 in words is "two hundred fifty-one million, two hundred fifteen thousand, five hundred sixty-one".