251891 has 4 divisors (see below), whose sum is σ = 252984. Its totient is φ = 250800.

The previous prime is 251887. The next prime is 251893. The reversal of 251891 is 198152.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 251891 - 2² = 251887 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 251891.

It is not an unprimeable number, because it can be changed into a prime (251893) 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, 50 + ... + 711.

It is an arithmetic number, because the mean of its divisors is an integer number (63246).

2²⁵¹⁸⁹¹ is an apocalyptic number.

251891 is a deficient number, since it is larger than the sum of its proper divisors (1093).

251891 is an equidigital number, since it uses as much as digits as its factorization.

251891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1092.

The product of its digits is 720, while the sum is 26.

The square root of 251891 is about 501.8874375794. The cubic root of 251891 is about 63.1544877426.

The spelling of 251891 in words is "two hundred fifty-one thousand, eight hundred ninety-one".