661666786560 has 1440 divisors, whose sum is σ = 2746317353472. Its totient is φ = 150652846080.

The previous prime is 661666786553. The next prime is 661666786579. The reversal of 661666786560 is 65687666166.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (1440).

It is a congruent number.

It is an unprimeable number.

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 159 ways as a sum of consecutive naturals, for example, 1535189545 + ... + 1535189975.

Almost surely, 2^661666786560 is an apocalyptic number.

661666786560 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 661666786560, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1373158676736).

661666786560 is an abundant number, since it is smaller than the sum of its proper divisors (2084650566912).

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

661666786560 is a wasteful number, since it uses less digits than its factorization.

661666786560 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 561 (or 538 counting only the distinct ones).

The product of its (nonzero) digits is 78382080, while the sum is 63.

The spelling of 661666786560 in words is "six hundred sixty-one billion, six hundred sixty-six million, seven hundred eighty-six thousand, five hundred sixty".