251091 has 12 divisors (see below), whose sum is σ = 378768. Its totient is φ = 159984.

The previous prime is 251087. The next prime is 251099. The reversal of 251091 is 190152.

251091 is nontrivially palindromic in base 16.

It is not a de Polignac number, because 251091 - 2² = 251087 is a prime.

It is a Smith number, since the sum of its digits (18) coincides with the sum of the digits of its prime factors.

It is not an unprimeable number, because it can be changed into a prime (251099) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 400 + ... + 813.

It is an arithmetic number, because the mean of its divisors is an integer number (31564).

2²⁵¹⁰⁹¹ is an apocalyptic number.

251091 is a deficient number, since it is larger than the sum of its proper divisors (127677).

251091 is a wasteful number, since it uses less digits than its factorization.

251091 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1242 (or 1239 counting only the distinct ones).

The product of its (nonzero) digits is 90, while the sum is 18.

The square root of 251091 is about 501.0898123091. The cubic root of 251091 is about 63.0875577716.

Subtracting from 251091 its product of nonzero digits (90), we obtain a square (251001 = 501²).

It can be divided in two parts, 2510 and 91, that added together give a square (2601 = 51²).

The spelling of 251091 in words is "two hundred fifty-one thousand, ninety-one".