251391 has 8 divisors (see below), whose sum is σ = 383104. Its totient is φ = 143640.

The previous prime is 251387. The next prime is 251393. The reversal of 251391 is 193152.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 251391 - 2² = 251387 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21), and also a Moran number because the ratio is a prime number: 11971 = 251391 / (2 + 5 + 1 + 3 + 9 + 1).

It is a Duffinian number.

It is a zygodrome in base 4.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 251391.

It is not an unprimeable number, because it can be changed into a prime (251393) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5965 + ... + 6006.

It is an arithmetic number, because the mean of its divisors is an integer number (47888).

2²⁵¹³⁹¹ is an apocalyptic number.

251391 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

251391 is a deficient number, since it is larger than the sum of its proper divisors (131713).

251391 is a wasteful number, since it uses less digits than its factorization.

251391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11981.

The product of its digits is 270, while the sum is 21.

The square root of 251391 is about 501.3890704832. The cubic root of 251391 is about 63.1126731477.

The spelling of 251391 in words is "two hundred fifty-one thousand, three hundred ninety-one".