251640 has 64 divisors (see below), whose sum is σ = 842400. Its totient is φ = 66816.

The previous prime is 251639. The next prime is 251653. The reversal of 251640 is 46152.

It is a happy number.

251640 is a `hidden beast` number, since 25 + 1 + 640 = 666.

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

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a nialpdrome in base 6.

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 251640.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 964 + ... + 1196.

2²⁵¹⁶⁴⁰ is an apocalyptic number.

251640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 251640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (421200).

251640 is an abundant number, since it is smaller than the sum of its proper divisors (590760).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

251640 is a wasteful number, since it uses less digits than its factorization.

251640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 253 (or 243 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 18.

The square root of 251640 is about 501.6373191859. The cubic root of 251640 is about 63.1335037395.

Adding to 251640 its reverse (46152), we get a palindrome (297792).

It can be divided in two parts, 2516 and 40, that added together give a triangular number (2556 = T₇₁).

The spelling of 251640 in words is "two hundred fifty-one thousand, six hundred forty".