251121661 has 4 divisors (see below), whose sum is σ = 286996192. Its totient is φ = 215247132.

The previous prime is 251121649. The next prime is 251121697. The reversal of 251121661 is 166121152.

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 a de Polignac number, because none of the positive numbers 2^k-251121661 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (251121601) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 17937255 + ... + 17937268.

It is an arithmetic number, because the mean of its divisors is an integer number (71749048).

Almost surely, 2^251121661 is an apocalyptic number.

It is an amenable number.

251121661 is a deficient number, since it is larger than the sum of its proper divisors (35874531).

251121661 is an equidigital number, since it uses as much as digits as its factorization.

251121661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 35874530.

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

The square root of 251121661 is about 15846.8186397144. The cubic root of 251121661 is about 630.9012556423.

The spelling of 251121661 in words is "two hundred fifty-one million, one hundred twenty-one thousand, six hundred sixty-one".