666521603 has 12 divisors (see below), whose sum is σ = 735267624. Its totient is φ = 603741600.

The previous prime is 666521599. The next prime is 666521627. The reversal of 666521603 is 306125666.

It is not a de Polignac number, because 666521603 - 2² = 666521599 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (666521503) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 24200 + ... + 43802.

It is an arithmetic number, because the mean of its divisors is an integer number (61272302).

Almost surely, 2^666521603 is an apocalyptic number.

666521603 is a deficient number, since it is larger than the sum of its proper divisors (68746021).

666521603 is a wasteful number, since it uses less digits than its factorization.

666521603 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19906 (or 19895 counting only the distinct ones).

The product of its (nonzero) digits is 38880, while the sum is 35.

The square root of 666521603 is about 25817.0796760594. The cubic root of 666521603 is about 873.5170977473.

The spelling of 666521603 in words is "six hundred sixty-six million, five hundred twenty-one thousand, six hundred three".