666658821 has 16 divisors (see below), whose sum is σ = 894748608. Its totient is φ = 441513600.

The previous prime is 666658793. The next prime is 666658879. The reversal of 666658821 is 128856666.

It is a happy number.

It is not a de Polignac number, because 666658821 - 2⁷ = 666658693 is a prime.

It is a super-2 number, since 2×666658821² = 888867967234220082, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (666658721) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 449401 + ... + 450881.

It is an arithmetic number, because the mean of its divisors is an integer number (55921788).

Almost surely, 2^666658821 is an apocalyptic number.

It is an amenable number.

666658821 is a deficient number, since it is larger than the sum of its proper divisors (228089787).

666658821 is a wasteful number, since it uses less digits than its factorization.

666658821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2372.

The product of its digits is 829440, while the sum is 48.

The square root of 666658821 is about 25819.7370435874. The cubic root of 666658821 is about 873.5770378123.

The spelling of 666658821 in words is "six hundred sixty-six million, six hundred fifty-eight thousand, eight hundred twenty-one".