251681 has 4 divisors (see below), whose sum is σ = 254100. Its totient is φ = 249264.

The previous prime is 251677. The next prime is 251701. The reversal of 251681 is 186152.

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 193600 + 58081 = 440^2 + 241^2 .

It is a cyclic number.

It is not a de Polignac number, because 251681 - 2² = 251677 is a prime.

It is a super-2 number, since 2×251681² = 126686651522, which contains 22 as substring.

It is a Duffinian number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 251681.

It is not an unprimeable number, because it can be changed into a prime (251611) 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, 1046 + ... + 1263.

It is an arithmetic number, because the mean of its divisors is an integer number (63525).

2²⁵¹⁶⁸¹ is an apocalyptic number.

It is an amenable number.

251681 is a deficient number, since it is larger than the sum of its proper divisors (2419).

251681 is a wasteful number, since it uses less digits than its factorization.

251681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2418.

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

The square root of 251681 is about 501.6781836995. The cubic root of 251681 is about 63.1369323586.

It can be divided in two parts, 25 and 1681, that multiplied together give a square (42025 = 205²).

The spelling of 251681 in words is "two hundred fifty-one thousand, six hundred eighty-one".