681593981 has 2 divisors, whose sum is σ = 681593982. Its totient is φ = 681593980.

The previous prime is 681593921. The next prime is 681593987. The reversal of 681593981 is 189395186.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 525968356 + 155625625 = 22934^2 + 12475^2 .

It is a cyclic number.

It is not a de Polignac number, because 681593981 - 2²⁶ = 614485117 is a prime.

It is a super-2 number, since 2×681593981² = 929140709870856722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (681593987) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 340796990 + 340796991.

It is an arithmetic number, because the mean of its divisors is an integer number (340796991).

Almost surely, 2^681593981 is an apocalyptic number.

It is an amenable number.

681593981 is a deficient number, since it is larger than the sum of its proper divisors (1).

681593981 is an equidigital number, since it uses as much as digits as its factorization.

681593981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 466560, while the sum is 50.

The square root of 681593981 is about 26107.3549215542. The cubic root of 681593981 is about 880.0525024633.

The spelling of 681593981 in words is "six hundred eighty-one million, five hundred ninety-three thousand, nine hundred eighty-one".