666516561 has 16 divisors (see below), whose sum is σ = 950802240. Its totient is φ = 414054720.

The previous prime is 666516553. The next prime is 666516577. The reversal of 666516561 is 165615666.

It is not a de Polignac number, because 666516561 - 2³ = 666516553 is a prime.

It is not an unprimeable number, because it can be changed into a prime (666516761) 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, 92370 + ... + 99323.

It is an arithmetic number, because the mean of its divisors is an integer number (59425140).

Almost surely, 2^666516561 is an apocalyptic number.

666516561 is a gapful number since it is divisible by the number (61) formed by its first and last digit.

It is an amenable number.

666516561 is a deficient number, since it is larger than the sum of its proper divisors (284285679).

666516561 is a wasteful number, since it uses less digits than its factorization.

666516561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 191776.

The product of its digits is 194400, while the sum is 42.

The square root of 666516561 is about 25816.9820273401. The cubic root of 666516561 is about 873.5148951258.

The spelling of 666516561 in words is "six hundred sixty-six million, five hundred sixteen thousand, five hundred sixty-one".