661981786472916 has 864 divisors, whose sum is σ = 2137144535285760. Its totient is φ = 169069320935424.

The previous prime is 661981786472843. The next prime is 661981786472921. The reversal of 661981786472916 is 619274687189166.

661981786472916 is a `hidden beast` number, since 6 + 61 + 9 + 8 + 1 + 7 + 86 + 472 + 9 + 1 + 6 = 666.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 287 ways as a sum of consecutive naturals, for example, 320883075301 + ... + 320883077363.

It is an arithmetic number, because the mean of its divisors is an integer number (2473546915840).

Almost surely, 2^{661981786472916} 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 661981786472916, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1068572267642880).

661981786472916 is an abundant number, since it is smaller than the sum of its proper divisors (1475162748812844).

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

661981786472916 is a wasteful number, since it uses less digits than its factorization.

661981786472916 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3565 (or 3547 counting only the distinct ones).

The product of its digits is 2633637888, while the sum is 81.

The spelling of 661981786472916 in words is "six hundred sixty-one trillion, nine hundred eighty-one billion, seven hundred eighty-six million, four hundred seventy-two thousand, nine hundred sixteen".