660559981 has 2 divisors, whose sum is σ = 660559982. Its totient is φ = 660559980.

The previous prime is 660559967. The next prime is 660560029. The reversal of 660559981 is 189955066.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 645668100 + 14891881 = 25410^2 + 3859^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-660559981 is a prime.

It is a super-2 number, since 2×660559981² = 872678976997440722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (660559181) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330279990 + 330279991.

It is an arithmetic number, because the mean of its divisors is an integer number (330279991).

Almost surely, 2^660559981 is an apocalyptic number.

It is an amenable number.

660559981 is a deficient number, since it is larger than the sum of its proper divisors (1).

660559981 is an equidigital number, since it uses as much as digits as its factorization.

660559981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 583200, while the sum is 49.

The square root of 660559981 is about 25701.3614619926. The cubic root of 660559981 is about 870.9049380791.

The spelling of 660559981 in words is "six hundred sixty million, five hundred fifty-nine thousand, nine hundred eighty-one".