666565621 has 2 divisors, whose sum is σ = 666565622. Its totient is φ = 666565620.

The previous prime is 666565567. The next prime is 666565639. The reversal of 666565621 is 126565666.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 447111025 + 219454596 = 21145^2 + 14814^2 .

It is a cyclic number.

It is not a de Polignac number, because 666565621 - 2²⁹ = 129694709 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (666565651) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 333282810 + 333282811.

It is an arithmetic number, because the mean of its divisors is an integer number (333282811).

Almost surely, 2^666565621 is an apocalyptic number.

It is an amenable number.

666565621 is a deficient number, since it is larger than the sum of its proper divisors (1).

666565621 is an equidigital number, since it uses as much as digits as its factorization.

666565621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 388800, while the sum is 43.

The square root of 666565621 is about 25817.9321596444. The cubic root of 666565621 is about 873.5363267460.

The spelling of 666565621 in words is "six hundred sixty-six million, five hundred sixty-five thousand, six hundred twenty-one".