666615021 has 16 divisors (see below), whose sum is σ = 895134720. Its totient is φ = 441262080.

The previous prime is 666615013. The next prime is 666615091. The reversal of 666615021 is 120516666.

It is not a de Polignac number, because 666615021 - 2³ = 666615013 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (666615091) 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, 577581 + ... + 578733.

It is an arithmetic number, because the mean of its divisors is an integer number (55945920).

Almost surely, 2^666615021 is an apocalyptic number.

It is an amenable number.

666615021 is a deficient number, since it is larger than the sum of its proper divisors (228519699).

666615021 is a wasteful number, since it uses less digits than its factorization.

666615021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2356.

The product of its (nonzero) digits is 12960, while the sum is 33.

The square root of 666615021 is about 25818.8888413115. Note that the first 4 decimals coincide. The cubic root of 666615021 is about 873.5579058310.

The spelling of 666615021 in words is "six hundred sixty-six million, six hundred fifteen thousand, twenty-one".