66551615556561 has 8 divisors (see below), whose sum is σ = 98594986009760. Its totient is φ = 44367743704356.

The previous prime is 66551615556539. The next prime is 66551615556563. The reversal of 66551615556561 is 16565551615566.

66551615556561 is a `hidden beast` number, since 6 + 6 + 5 + 5 + 1 + 6 + 1 + 5 + 5 + 565 + 61 = 666.

66551615556561 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 66551615556561 - 2⁵ = 66551615556529 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66551615556563) 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 7 ways as a sum of consecutive naturals, for example, 1232437325095 + ... + 1232437325148.

It is an arithmetic number, because the mean of its divisors is an integer number (12324373251220).

Almost surely, 2^{66551615556561} is an apocalyptic number.

It is an amenable number.

66551615556561 is a deficient number, since it is larger than the sum of its proper divisors (32043370453199).

66551615556561 is a wasteful number, since it uses less digits than its factorization.

66551615556561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2464874650252 (or 2464874650246 counting only the distinct ones).

The product of its digits is 121500000, while the sum is 63.

The spelling of 66551615556561 in words is "sixty-six trillion, five hundred fifty-one billion, six hundred fifteen million, five hundred fifty-six thousand, five hundred sixty-one".