257155721 has 2 divisors, whose sum is σ = 257155722. Its totient is φ = 257155720.

The previous prime is 257155711. The next prime is 257155729. The reversal of 257155721 is 127551752.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 162307600 + 94848121 = 12740^2 + 9739^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-257155721 is a prime.

It is a super-2 number, since 2×257155721² = 132258129686059682, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (257155729) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 128577860 + 128577861.

It is an arithmetic number, because the mean of its divisors is an integer number (128577861).

Almost surely, 2^257155721 is an apocalyptic number.

It is an amenable number.

257155721 is a deficient number, since it is larger than the sum of its proper divisors (1).

257155721 is an equidigital number, since it uses as much as digits as its factorization.

257155721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 24500, while the sum is 35.

The square root of 257155721 is about 16036.0756109467. The cubic root of 257155721 is about 635.9145035252.

The spelling of 257155721 in words is "two hundred fifty-seven million, one hundred fifty-five thousand, seven hundred twenty-one".