256720781 has 4 divisors (see below), whose sum is σ = 256752864. Its totient is φ = 256688700.

The previous prime is 256720769. The next prime is 256720787. The reversal of 256720781 is 187027652.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-256720781 is a prime.

It is a super-2 number, since 2×256720781² = 131811118794499922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (256720787) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6866 + ... + 23676.

It is an arithmetic number, because the mean of its divisors is an integer number (64188216).

Almost surely, 2^256720781 is an apocalyptic number.

It is an amenable number.

256720781 is a deficient number, since it is larger than the sum of its proper divisors (32083).

256720781 is a wasteful number, since it uses less digits than its factorization.

256720781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 32082.

The product of its (nonzero) digits is 47040, while the sum is 38.

The square root of 256720781 is about 16022.5085738782. The cubic root of 256720781 is about 635.5557834814. Note that the first 3 decimals are identical.

The spelling of 256720781 in words is "two hundred fifty-six million, seven hundred twenty thousand, seven hundred eighty-one".