664637621 has 2 divisors, whose sum is σ = 664637622. Its totient is φ = 664637620.

The previous prime is 664637587. The next prime is 664637641. The reversal of 664637621 is 126736466.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 478996996 + 185640625 = 21886^2 + 13625^2 .

It is a cyclic number.

It is not a de Polignac number, because 664637621 - 2¹⁰ = 664636597 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (664637641) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332318810 + 332318811.

It is an arithmetic number, because the mean of its divisors is an integer number (332318811).

Almost surely, 2^664637621 is an apocalyptic number.

It is an amenable number.

664637621 is a deficient number, since it is larger than the sum of its proper divisors (1).

664637621 is an equidigital number, since it uses as much as digits as its factorization.

664637621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 217728, while the sum is 41.

The square root of 664637621 is about 25780.5667315519. The cubic root of 664637621 is about 872.6932967462.

The spelling of 664637621 in words is "six hundred sixty-four million, six hundred thirty-seven thousand, six hundred twenty-one".