256421681 has 2 divisors, whose sum is σ = 256421682. Its totient is φ = 256421680.

The previous prime is 256421623. The next prime is 256421689. The reversal of 256421681 is 186124652.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 241336225 + 15085456 = 15535^2 + 3884^2 .

It is a cyclic number.

It is not a de Polignac number, because 256421681 - 2¹⁸ = 256159537 is a prime.

It is a super-2 number, since 2×256421681² = 131504156973731522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (256421689) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 128210840 + 128210841.

It is an arithmetic number, because the mean of its divisors is an integer number (128210841).

Almost surely, 2^256421681 is an apocalyptic number.

It is an amenable number.

256421681 is a deficient number, since it is larger than the sum of its proper divisors (1).

256421681 is an equidigital number, since it uses as much as digits as its factorization.

256421681 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 23040, while the sum is 35.

The square root of 256421681 is about 16013.1721092356. The cubic root of 256421681 is about 635.3088633229.

The spelling of 256421681 in words is "two hundred fifty-six million, four hundred twenty-one thousand, six hundred eighty-one".