251887788661 has 4 divisors (see below), whose sum is σ = 252535315500. Its totient is φ = 251240261824.

The previous prime is 251887788653. The next prime is 251887788667. The reversal of 251887788661 is 166887788152.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 56373479761 + 195514308900 = 237431^2 + 442170^2 .

It is a cyclic number.

It is not a de Polignac number, because 251887788661 - 2³ = 251887788653 is a prime.

It is a super-4 number, since 4×251887788661⁴ (a number of 47 digits) contains 4444 as substring.

It is a Smith number, since the sum of its digits (67) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (251887788667) 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, 323762836 + ... + 323763613.

It is an arithmetic number, because the mean of its divisors is an integer number (63133828875).

Almost surely, 2^251887788661 is an apocalyptic number.

It is an amenable number.

251887788661 is a deficient number, since it is larger than the sum of its proper divisors (647526839).

251887788661 is an equidigital number, since it uses as much as digits as its factorization.

251887788661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 647526838.

The product of its digits is 72253440, while the sum is 67.

The spelling of 251887788661 in words is "two hundred fifty-one billion, eight hundred eighty-seven million, seven hundred eighty-eight thousand, six hundred sixty-one".