251397561 has 4 divisors (see below), whose sum is σ = 335196752. Its totient is φ = 167598372.

The previous prime is 251397539. The next prime is 251397563. The reversal of 251397561 is 165793152.

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 251397561 - 2¹⁵ = 251364793 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (251397563) 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, 41899591 + ... + 41899596.

It is an arithmetic number, because the mean of its divisors is an integer number (83799188).

Almost surely, 2^251397561 is an apocalyptic number.

It is an amenable number.

251397561 is a deficient number, since it is larger than the sum of its proper divisors (83799191).

251397561 is an equidigital number, since it uses as much as digits as its factorization.

251397561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 83799190.

The product of its digits is 56700, while the sum is 39.

The square root of 251397561 is about 15855.5214672996. The cubic root of 251397561 is about 631.1322219764.

The spelling of 251397561 in words is "two hundred fifty-one million, three hundred ninety-seven thousand, five hundred sixty-one".