665999217 has 12 divisors (see below), whose sum is σ = 1035998964. Its totient is φ = 409845600.

The previous prime is 665999207. The next prime is 665999227. The reversal of 665999217 is 712999566.

It is an interprime number because it is at equal distance from previous prime (665999207) and next prime (665999227).

It can be written as a sum of positive squares in 2 ways, for example, as 210134016 + 455865201 = 14496^2 + 21351^2 .

It is not a de Polignac number, because 665999217 - 2¹⁴ = 665982833 is a prime.

It is a super-2 number, since 2×665999217² = 887109914089226178, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (665999207) 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 in 11 ways as a sum of consecutive naturals, for example, 2846034 + ... + 2846267.

It is an arithmetic number, because the mean of its divisors is an integer number (86333247).

Almost surely, 2^665999217 is an apocalyptic number.

It is an amenable number.

665999217 is a deficient number, since it is larger than the sum of its proper divisors (369999747).

665999217 is a wasteful number, since it uses less digits than its factorization.

665999217 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5692320 (or 5692317 counting only the distinct ones).

The product of its digits is 1837080, while the sum is 54.

The square root of 665999217 is about 25806.9606308066. The cubic root of 665999217 is about 873.2888318945.

The spelling of 665999217 in words is "six hundred sixty-five million, nine hundred ninety-nine thousand, two hundred seventeen".