256736561 has 2 divisors, whose sum is σ = 256736562. Its totient is φ = 256736560.

The previous prime is 256736489. The next prime is 256736587. The reversal of 256736561 is 165637652.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 235438336 + 21298225 = 15344^2 + 4615^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-256736561 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (256736591) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 128368280 + 128368281.

It is an arithmetic number, because the mean of its divisors is an integer number (128368281).

Almost surely, 2^256736561 is an apocalyptic number.

It is an amenable number.

256736561 is a deficient number, since it is larger than the sum of its proper divisors (1).

256736561 is an equidigital number, since it uses as much as digits as its factorization.

256736561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 226800, while the sum is 41.

The square root of 256736561 is about 16023.0009985645. Note that the first 3 decimals coincide. The cubic root of 256736561 is about 635.5688052356.

The spelling of 256736561 in words is "two hundred fifty-six million, seven hundred thirty-six thousand, five hundred sixty-one".