256421 has 4 divisors (see below), whose sum is σ = 279744. Its totient is φ = 233100.

The previous prime is 256393. The next prime is 256423. The reversal of 256421 is 124652.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-256421 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 256393 and 256402.

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 256421.

It is not an unprimeable number, because it can be changed into a prime (256423) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 11645 + ... + 11666.

It is an arithmetic number, because the mean of its divisors is an integer number (69936).

2²⁵⁶⁴²¹ is an apocalyptic number.

It is an amenable number.

256421 is a deficient number, since it is larger than the sum of its proper divisors (23323).

256421 is a wasteful number, since it uses less digits than its factorization.

256421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23322.

The product of its digits is 480, while the sum is 20.

The square root of 256421 is about 506.3802918756. The cubic root of 256421 is about 63.5308300909.

Subtracting from 256421 its reverse (124652), we obtain a square (131769 = 363²).

It can be divided in two parts, 25 and 6421, that added together give a palindrome (6446).

The spelling of 256421 in words is "two hundred fifty-six thousand, four hundred twenty-one".