666355021 has 2 divisors, whose sum is σ = 666355022. Its totient is φ = 666355020.

The previous prime is 666355009. The next prime is 666355073. The reversal of 666355021 is 120553666.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 464402500 + 201952521 = 21550^2 + 14211^2 .

It is a cyclic number.

It is not a de Polignac number, because 666355021 - 2⁵ = 666354989 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (666355321) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 333177510 + 333177511.

It is an arithmetic number, because the mean of its divisors is an integer number (333177511).

Almost surely, 2^666355021 is an apocalyptic number.

It is an amenable number.

666355021 is a deficient number, since it is larger than the sum of its proper divisors (1).

666355021 is an equidigital number, since it uses as much as digits as its factorization.

666355021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 32400, while the sum is 34.

The square root of 666355021 is about 25813.8532768744. The cubic root of 666355021 is about 873.4443197364. Note that the first 3 decimals are identical.

The spelling of 666355021 in words is "six hundred sixty-six million, three hundred fifty-five thousand, twenty-one".