256121021 has 6 divisors (see below), whose sum is σ = 277338330. Its totient is φ = 236419248.

The previous prime is 256120981. The next prime is 256121023. The reversal of 256121021 is 120121652.

256121021 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 3 ways, for example, as 21724921 + 234396100 = 4661^2 + 15310^2 .

It is not a de Polignac number, because 256121021 - 2⁶ = 256120957 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 256120984 and 256121002.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (256121023) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 757586 + ... + 757923.

It is an arithmetic number, because the mean of its divisors is an integer number (46223055).

Almost surely, 2^256121021 is an apocalyptic number.

It is an amenable number.

256121021 is a deficient number, since it is larger than the sum of its proper divisors (21217309).

256121021 is a wasteful number, since it uses less digits than its factorization.

256121021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1515535 (or 1515522 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 20.

The square root of 256121021 is about 16003.7814593927. The cubic root of 256121021 is about 635.0604617239.

Adding to 256121021 its reverse (120121652), we get a palindrome (376242673).

The spelling of 256121021 in words is "two hundred fifty-six million, one hundred twenty-one thousand, twenty-one".