256991257 has 2 divisors, whose sum is σ = 256991258. Its totient is φ = 256991256.

The previous prime is 256991237. The next prime is 256991299. The reversal of 256991257 is 752199652.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 161264601 + 95726656 = 12699^2 + 9784^2 .

It is a cyclic number.

It is not a de Polignac number, because 256991257 - 2²³ = 248602649 is a prime.

It is not a weakly prime, because it can be changed into another prime (256991237) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 128495628 + 128495629.

It is an arithmetic number, because the mean of its divisors is an integer number (128495629).

Almost surely, 2^256991257 is an apocalyptic number.

It is an amenable number.

256991257 is a deficient number, since it is larger than the sum of its proper divisors (1).

256991257 is an equidigital number, since it uses as much as digits as its factorization.

256991257 is an evil number, because the sum of its binary digits is even.

The product of its digits is 340200, while the sum is 46.

The square root of 256991257 is about 16030.9468528843. The cubic root of 256991257 is about 635.7789081925.

The spelling of 256991257 in words is "two hundred fifty-six million, nine hundred ninety-one thousand, two hundred fifty-seven".