251211661 has 4 divisors (see below), whose sum is σ = 251252800. Its totient is φ = 251170524.

The previous prime is 251211641. The next prime is 251211683. The reversal of 251211661 is 166112152.

It is a happy number.

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 251211661 - 2⁵ = 251211629 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (251211641) 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, 9381 + ... + 24298.

It is an arithmetic number, because the mean of its divisors is an integer number (62813200).

Almost surely, 2^251211661 is an apocalyptic number.

It is an amenable number.

251211661 is a deficient number, since it is larger than the sum of its proper divisors (41139).

251211661 is an equidigital number, since it uses as much as digits as its factorization.

251211661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 41138.

The product of its digits is 720, while the sum is 25.

The square root of 251211661 is about 15849.6580720216. The cubic root of 251211661 is about 630.9766166324.

The spelling of 251211661 in words is "two hundred fifty-one million, two hundred eleven thousand, six hundred sixty-one".