251981 has 4 divisors (see below), whose sum is σ = 260700. Its totient is φ = 243264.

The previous prime is 251971. The next prime is 251983. The reversal of 251981 is 189152.

It is a happy number.

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 184900 + 67081 = 430^2 + 259^2 .

It is a cyclic number.

It is not a de Polignac number, because 251981 - 2⁶ = 251917 is a prime.

It is a super-2 number, since 2×251981² = 126988848722, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 251981.

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 251981.

It is not an unprimeable number, because it can be changed into a prime (251983) 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, 4316 + ... + 4373.

It is an arithmetic number, because the mean of its divisors is an integer number (65175).

2²⁵¹⁹⁸¹ is an apocalyptic number.

It is an amenable number.

251981 is a deficient number, since it is larger than the sum of its proper divisors (8719).

251981 is an equidigital number, since it uses as much as digits as its factorization.

251981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8718.

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

The square root of 251981 is about 501.9770911107. The cubic root of 251981 is about 63.1620084918.

The spelling of 251981 in words is "two hundred fifty-one thousand, nine hundred eighty-one".