665603921 has 2 divisors, whose sum is σ = 665603922. Its totient is φ = 665603920.

The previous prime is 665603899. The next prime is 665603971. The reversal of 665603921 is 129306566.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 606144400 + 59459521 = 24620^2 + 7711^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-665603921 is a prime.

It is not a weakly prime, because it can be changed into another prime (665603971) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332801960 + 332801961.

It is an arithmetic number, because the mean of its divisors is an integer number (332801961).

Almost surely, 2^665603921 is an apocalyptic number.

It is an amenable number.

665603921 is a deficient number, since it is larger than the sum of its proper divisors (1).

665603921 is an equidigital number, since it uses as much as digits as its factorization.

665603921 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 58320, while the sum is 38.

The square root of 665603921 is about 25799.3007850988. The cubic root of 665603921 is about 873.1160209293.

The spelling of 665603921 in words is "six hundred sixty-five million, six hundred three thousand, nine hundred twenty-one".