681555896521 has 2 divisors, whose sum is σ = 681555896522. Its totient is φ = 681555896520.

The previous prime is 681555896503. The next prime is 681555896557. The reversal of 681555896521 is 125698555186.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 342267121296 + 339288775225 = 585036^2 + 582485^2 .

It is a cyclic number.

It is not a de Polignac number, because 681555896521 - 2²⁵ = 681522342089 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 681555896521.

It is not a weakly prime, because it can be changed into another prime (681555896621) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 340777948260 + 340777948261.

It is an arithmetic number, because the mean of its divisors is an integer number (340777948261).

Almost surely, 2^681555896521 is an apocalyptic number.

It is an amenable number.

681555896521 is a deficient number, since it is larger than the sum of its proper divisors (1).

681555896521 is an equidigital number, since it uses as much as digits as its factorization.

681555896521 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 25920000, while the sum is 61.

The spelling of 681555896521 in words is "six hundred eighty-one billion, five hundred fifty-five million, eight hundred ninety-six thousand, five hundred twenty-one".