666947217 has 4 divisors (see below), whose sum is σ = 889262960. Its totient is φ = 444631476.

The previous prime is 666947173. The next prime is 666947273. The reversal of 666947217 is 712749666.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 666947217 - 2⁸ = 666946961 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (666947297) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 111157867 + ... + 111157872.

It is an arithmetic number, because the mean of its divisors is an integer number (222315740).

Almost surely, 2^666947217 is an apocalyptic number.

It is an amenable number.

666947217 is a deficient number, since it is larger than the sum of its proper divisors (222315743).

666947217 is a wasteful number, since it uses less digits than its factorization.

666947217 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 222315742.

The product of its digits is 762048, while the sum is 48.

The square root of 666947217 is about 25825.3212371115. The cubic root of 666947217 is about 873.7029891961.

The spelling of 666947217 in words is "six hundred sixty-six million, nine hundred forty-seven thousand, two hundred seventeen".