6661647720 has 384 divisors, whose sum is σ = 27272044800. Its totient is φ = 1372557312.

The previous prime is 6661647719. The next prime is 6661647737. The reversal of 6661647720 is 277461666.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is an unprimeable number.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 1406316 + ... + 1411044.

It is an arithmetic number, because the mean of its divisors is an integer number (71020950).

Almost surely, 2^6661647720 is an apocalyptic number.

6661647720 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 6661647720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (13636022400).

6661647720 is an abundant number, since it is smaller than the sum of its proper divisors (20610397080).

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

6661647720 is a wasteful number, since it uses less digits than its factorization.

6661647720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4809 (or 4802 counting only the distinct ones).

The product of its (nonzero) digits is 508032, while the sum is 45.

The square root of 6661647720 is about 81618.9176600621. The cubic root of 6661647720 is about 1881.5996382258.

The spelling of 6661647720 in words is "six billion, six hundred sixty-one million, six hundred forty-seven thousand, seven hundred twenty".