666521726521 has 32 divisors (see below), whose sum is σ = 780142067712. Its totient is φ = 557688606720.

The previous prime is 666521726509. The next prime is 666521726527. The reversal of 666521726521 is 125627125666.

It is a de Polignac number, because none of the positive numbers 2^k-666521726521 is a prime.

It is not an unprimeable number, because it can be changed into a prime (666521726527) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 21315120 + ... + 21346366.

It is an arithmetic number, because the mean of its divisors is an integer number (24379439616).

Almost surely, 2^666521726521 is an apocalyptic number.

It is an amenable number.

666521726521 is a deficient number, since it is larger than the sum of its proper divisors (113620341191).

666521726521 is a wasteful number, since it uses less digits than its factorization.

666521726521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 31749.

The product of its digits is 1814400, while the sum is 49.

The spelling of 666521726521 in words is "six hundred sixty-six billion, five hundred twenty-one million, seven hundred twenty-six thousand, five hundred twenty-one".