251231561 has 4 divisors (see below), whose sum is σ = 287121792. Its totient is φ = 215341332.

The previous prime is 251231543. The next prime is 251231579. The reversal of 251231561 is 165132152.

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 an interprime number because it is at equal distance from previous prime (251231543) and next prime (251231579).

It is a cyclic number.

It is not a de Polignac number, because 251231561 - 2¹⁸ = 250969417 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 251231561.

It is not an unprimeable number, because it can be changed into a prime (251231861) 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, 17945105 + ... + 17945118.

It is an arithmetic number, because the mean of its divisors is an integer number (71780448).

Almost surely, 2^251231561 is an apocalyptic number.

It is an amenable number.

251231561 is a deficient number, since it is larger than the sum of its proper divisors (35890231).

251231561 is an equidigital number, since it uses as much as digits as its factorization.

251231561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 35890230.

The product of its digits is 1800, while the sum is 26.

The square root of 251231561 is about 15850.2858333848. The cubic root of 251231561 is about 630.9932773547.

The spelling of 251231561 in words is "two hundred fifty-one million, two hundred thirty-one thousand, five hundred sixty-one".