256821621 has 8 divisors (see below), whose sum is σ = 391347264. Its totient is φ = 146755200.

The previous prime is 256821619. The next prime is 256821637. The reversal of 256821621 is 126128652.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 256821621 - 2¹ = 256821619 is a prime.

It is a Smith number, since the sum of its digits (33) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (256821641) 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 in 7 ways as a sum of consecutive naturals, for example, 6114780 + ... + 6114821.

It is an arithmetic number, because the mean of its divisors is an integer number (48918408).

Almost surely, 2^256821621 is an apocalyptic number.

256821621 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

256821621 is a deficient number, since it is larger than the sum of its proper divisors (134525643).

256821621 is a wasteful number, since it uses less digits than its factorization.

256821621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12229611.

The product of its digits is 11520, while the sum is 33.

The square root of 256821621 is about 16025.6550880143. The cubic root of 256821621 is about 635.6389880890.

The spelling of 256821621 in words is "two hundred fifty-six million, eight hundred twenty-one thousand, six hundred twenty-one".