66516561 has 6 divisors (see below), whose sum is σ = 96079490. Its totient is φ = 44344368.

The previous prime is 66516559. The next prime is 66516581. The reversal of 66516561 is 16561566.

It can be written as a sum of positive squares in only one way, i.e., 51840000 + 14676561 = 7200^2 + 3831^2 .

It is not a de Polignac number, because 66516561 - 2¹ = 66516559 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66516521) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 3695356 + ... + 3695373.

Almost surely, 2^66516561 is an apocalyptic number.

It is an amenable number.

66516561 is a deficient number, since it is larger than the sum of its proper divisors (29562929).

66516561 is a wasteful number, since it uses less digits than its factorization.

66516561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7390735 (or 7390732 counting only the distinct ones).

The product of its digits is 32400, while the sum is 36.

The square root of 66516561 is about 8155.7685719986. The cubic root of 66516561 is about 405.1755800196.

The spelling of 66516561 in words is "sixty-six million, five hundred sixteen thousand, five hundred sixty-one".