66781217664 has 256 divisors, whose sum is σ = 228621657600. Its totient is φ = 18795110400.

The previous prime is 66781217611. The next prime is 66781217683. The reversal of 66781217664 is 46671218766.

It is a Harshad number since it is a multiple of its sum of digits (54).

It is a nude number because it is divisible by every one of its digits.

It is a self number, because there is not a number n which added to its sum of digits gives 66781217664.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 1600264 + ... + 1641464.

It is an arithmetic number, because the mean of its divisors is an integer number (893053350).

Almost surely, 2^66781217664 is an apocalyptic number.

66781217664 is a gapful number since it is divisible by the number (64) 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 66781217664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (114310828800).

66781217664 is an abundant number, since it is smaller than the sum of its proper divisors (161840439936).

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

66781217664 is a wasteful number, since it uses less digits than its factorization.

66781217664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 41298 (or 41280 counting only the distinct ones).

The product of its digits is 4064256, while the sum is 54.

The spelling of 66781217664 in words is "sixty-six billion, seven hundred eighty-one million, two hundred seventeen thousand, six hundred sixty-four".