251861 has 2 divisors, whose sum is σ = 251862. Its totient is φ = 251860.

The previous prime is 251857. The next prime is 251879. The reversal of 251861 is 168152.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 164836 + 87025 = 406^2 + 295^2 .

It is a cyclic number.

It is not a de Polignac number, because 251861 - 2² = 251857 is a prime.

It is a Chen prime.

It is a zygodrome in base 4.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (251831) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 125930 + 125931.

It is an arithmetic number, because the mean of its divisors is an integer number (125931).

2²⁵¹⁸⁶¹ is an apocalyptic number.

It is an amenable number.

251861 is a deficient number, since it is larger than the sum of its proper divisors (1).

251861 is an equidigital number, since it uses as much as digits as its factorization.

251861 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 480, while the sum is 23.

The square root of 251861 is about 501.8575495098. The cubic root of 251861 is about 63.1519804282.

The spelling of 251861 in words is "two hundred fifty-one thousand, eight hundred sixty-one".