256621051565381 has 2 divisors, whose sum is σ = 256621051565382. Its totient is φ = 256621051565380.

The previous prime is 256621051565369. The next prime is 256621051565387. The reversal of 256621051565381 is 183565150126652.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 152338762668481 + 104282288896900 = 12342559^2 + 10211870^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-256621051565381 is a prime.

It is a super-2 number, since 2×256621051565381² (a number of 30 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (256621051565387) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 128310525782690 + 128310525782691.

It is an arithmetic number, because the mean of its divisors is an integer number (128310525782691).

Almost surely, 2^{256621051565381} is an apocalyptic number.

It is an amenable number.

256621051565381 is a deficient number, since it is larger than the sum of its proper divisors (1).

256621051565381 is an equidigital number, since it uses as much as digits as its factorization.

256621051565381 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 12960000, while the sum is 56.

The spelling of 256621051565381 in words is "two hundred fifty-six trillion, six hundred twenty-one billion, fifty-one million, five hundred sixty-five thousand, three hundred eighty-one".