665939621 has 2 divisors, whose sum is σ = 665939622. Its totient is φ = 665939620.

The previous prime is 665939611. The next prime is 665939633. The reversal of 665939621 is 126939566.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 661055521 + 4884100 = 25711^2 + 2210^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-665939621 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (665939611) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332969810 + 332969811.

It is an arithmetic number, because the mean of its divisors is an integer number (332969811).

Almost surely, 2^665939621 is an apocalyptic number.

It is an amenable number.

665939621 is a deficient number, since it is larger than the sum of its proper divisors (1).

665939621 is an equidigital number, since it uses as much as digits as its factorization.

665939621 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 524880, while the sum is 47.

The square root of 665939621 is about 25805.8059552497. The cubic root of 665939621 is about 873.2627827780.

The spelling of 665939621 in words is "six hundred sixty-five million, nine hundred thirty-nine thousand, six hundred twenty-one".