66991686 has 16 divisors (see below), whose sum is σ = 139809024. Its totient is φ = 21359624.

The previous prime is 66991669. The next prime is 66991693. The reversal of 66991686 is 68619966.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 242586 + ... + 242861.

It is an arithmetic number, because the mean of its divisors is an integer number (8738064).

Almost surely, 2^66991686 is an apocalyptic number.

66991686 is an abundant number, since it is smaller than the sum of its proper divisors (72817338).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

66991686 is a wasteful number, since it uses less digits than its factorization.

66991686 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 485475.

The product of its digits is 839808, while the sum is 51.

The square root of 66991686 is about 8184.8448977363. The cubic root of 66991686 is about 406.1380094935.

It can be divided in two parts, 6699 and 1686, that added together give a triangular number (8385 = T₁₂₉).

The spelling of 66991686 in words is "sixty-six million, nine hundred ninety-one thousand, six hundred eighty-six".