256661 has 2 divisors, whose sum is σ = 256662. Its totient is φ = 256660.

The previous prime is 256651. The next prime is 256687. The reversal of 256661 is 166652.

It is an a-pointer prime, because the next prime (256687) can be obtained adding 256661 to its sum of digits (26).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 256036 + 625 = 506^2 + 25^2 .

It is a cyclic number.

It is not a de Polignac number, because 256661 - 2¹⁰ = 255637 is a prime.

It is a Chen prime.

It is a nialpdrome in base 4.

It is a zygodrome in base 4.

It is a self number, because there is not a number n which added to its sum of digits gives 256661.

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 256661.

It is not a weakly prime, because it can be changed into another prime (256651) 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 as a sum of consecutive naturals, namely, 128330 + 128331.

It is an arithmetic number, because the mean of its divisors is an integer number (128331).

2²⁵⁶⁶⁶¹ is an apocalyptic number.

It is an amenable number.

256661 is a deficient number, since it is larger than the sum of its proper divisors (1).

256661 is an equidigital number, since it uses as much as digits as its factorization.

256661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2160, while the sum is 26.

The square root of 256661 is about 506.6172124987. The cubic root of 256661 is about 63.5506446987.

Subtracting from 256661 its reverse (166652), we obtain a palindrome (90009).

The spelling of 256661 in words is "two hundred fifty-six thousand, six hundred sixty-one".