66405721688 has 32 divisors (see below), whose sum is σ = 130356097200. Its totient is φ = 31671685248.

The previous prime is 66405721673. The next prime is 66405721699. The reversal of 66405721688 is 88612750466.

It is a happy number.

It is a super-2 number, since 2×66405721688² (a number of 22 digits) contains 22 as substring.

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, 1705031 + ... + 1743542.

Almost surely, 2^66405721688 is an apocalyptic number.

It is an amenable number.

66405721688 is a deficient number, since it is larger than the sum of its proper divisors (63950375512).

66405721688 is a wasteful number, since it uses less digits than its factorization.

66405721688 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3448691 (or 3448687 counting only the distinct ones).

The product of its (nonzero) digits is 3870720, while the sum is 53.

The spelling of 66405721688 in words is "sixty-six billion, four hundred five million, seven hundred twenty-one thousand, six hundred eighty-eight".