251643 has 16 divisors (see below), whose sum is σ = 400896. Its totient is φ = 137280.

The previous prime is 251639. The next prime is 251653. The reversal of 251643 is 346152.

It is a happy number.

It is not a de Polignac number, because 251643 - 2² = 251639 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is not an unprimeable number, because it can be changed into a prime (251623) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 223 + ... + 743.

It is an arithmetic number, because the mean of its divisors is an integer number (25056).

2²⁵¹⁶⁴³ is an apocalyptic number.

251643 is a gapful number since it is divisible by the number (23) formed by its first and last digit.

251643 is a deficient number, since it is larger than the sum of its proper divisors (149253).

251643 is a wasteful number, since it uses less digits than its factorization.

251643 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 554.

The product of its digits is 720, while the sum is 21.

The square root of 251643 is about 501.6403093851. The cubic root of 251643 is about 63.1337546267.

Adding to 251643 its reverse (346152), we get a palindrome (597795).

The spelling of 251643 in words is "two hundred fifty-one thousand, six hundred forty-three".