664603981 has 2 divisors, whose sum is σ = 664603982. Its totient is φ = 664603980.

The previous prime is 664603943. The next prime is 664603987. The reversal of 664603981 is 189306466.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 657666025 + 6937956 = 25645^2 + 2634^2 .

It is a cyclic number.

It is not a de Polignac number, because 664603981 - 2²¹ = 662506829 is a prime.

It is a super-2 number, since 2×664603981² = 883396903122096722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (664603987) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332301990 + 332301991.

It is an arithmetic number, because the mean of its divisors is an integer number (332301991).

Almost surely, 2^664603981 is an apocalyptic number.

It is an amenable number.

664603981 is a deficient number, since it is larger than the sum of its proper divisors (1).

664603981 is an equidigital number, since it uses as much as digits as its factorization.

664603981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 186624, while the sum is 43.

The square root of 664603981 is about 25779.9142938839. The cubic root of 664603981 is about 872.6785729845.

The spelling of 664603981 in words is "six hundred sixty-four million, six hundred three thousand, nine hundred eighty-one".