661689191808 has 320 divisors, whose sum is σ = 2063784808800. Its totient is φ = 210050260992.

The previous prime is 661689191789. The next prime is 661689191881. The reversal of 661689191808 is 808191986166.

661689191808 is a `hidden beast` number, since 6 + 616 + 8 + 9 + 1 + 9 + 1 + 8 + 0 + 8 = 666.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 55556158 + ... + 55568066.

Almost surely, 2^661689191808 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 661689191808, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1031892404400).

661689191808 is an abundant number, since it is smaller than the sum of its proper divisors (1402095616992).

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

661689191808 is a wasteful number, since it uses less digits than its factorization.

661689191808 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12191 (or 12170 counting only the distinct ones).

The product of its (nonzero) digits is 8957952, while the sum is 63.

The spelling of 661689191808 in words is "six hundred sixty-one billion, six hundred eighty-nine million, one hundred ninety-one thousand, eight hundred eight".