664139981 has 2 divisors, whose sum is σ = 664139982. Its totient is φ = 664139980.

The previous prime is 664139977. The next prime is 664140073. The reversal of 664139981 is 189931466.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 403608100 + 260531881 = 20090^2 + 16141^2 .

It is a cyclic number.

It is not a de Polignac number, because 664139981 - 2² = 664139977 is a prime.

It is a super-2 number, since 2×664139981² = 882163828725360722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (664135981) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332069990 + 332069991.

It is an arithmetic number, because the mean of its divisors is an integer number (332069991).

Almost surely, 2^664139981 is an apocalyptic number.

It is an amenable number.

664139981 is a deficient number, since it is larger than the sum of its proper divisors (1).

664139981 is an equidigital number, since it uses as much as digits as its factorization.

664139981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 279936, while the sum is 47.

The square root of 664139981 is about 25770.9134684823. The cubic root of 664139981 is about 872.4754359086.

The spelling of 664139981 in words is "six hundred sixty-four million, one hundred thirty-nine thousand, nine hundred eighty-one".