666550309 has 2 divisors, whose sum is σ = 666550310. Its totient is φ = 666550308.

The previous prime is 666550303. The next prime is 666550321. The reversal of 666550309 is 903055666.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 434597409 + 231952900 = 20847^2 + 15230^2 .

It is a cyclic number.

It is not a de Polignac number, because 666550309 - 2⁵ = 666550277 is a prime.

It is a super-3 number, since 3×666550309³ (a number of 27 digits) contains 333 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (666550303) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 333275154 + 333275155.

It is an arithmetic number, because the mean of its divisors is an integer number (333275155).

Almost surely, 2^666550309 is an apocalyptic number.

It is an amenable number.

666550309 is a deficient number, since it is larger than the sum of its proper divisors (1).

666550309 is an equidigital number, since it uses as much as digits as its factorization.

666550309 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 145800, while the sum is 40.

The square root of 666550309 is about 25817.6356198626. The cubic root of 666550309 is about 873.5296378869.

The spelling of 666550309 in words is "six hundred sixty-six million, five hundred fifty thousand, three hundred nine".