256639 has 2 divisors, whose sum is σ = 256640. Its totient is φ = 256638.

The previous prime is 256609. The next prime is 256643. The reversal of 256639 is 936652.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 256639 - 2¹³ = 248447 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 256639.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (256609) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 128319 + 128320.

It is an arithmetic number, because the mean of its divisors is an integer number (128320).

2²⁵⁶⁶³⁹ is an apocalyptic number.

256639 is a deficient number, since it is larger than the sum of its proper divisors (1).

256639 is an equidigital number, since it uses as much as digits as its factorization.

256639 is an evil number, because the sum of its binary digits is even.

The product of its digits is 9720, while the sum is 31.

The square root of 256639 is about 506.5954993878. The cubic root of 256639 is about 63.5488288741.

The spelling of 256639 in words is "two hundred fifty-six thousand, six hundred thirty-nine".