661663660 has 72 divisors (see below), whose sum is σ = 1646976240. Its totient is φ = 222558336.

The previous prime is 661663649. The next prime is 661663663. The reversal of 661663660 is 66366166.

It is a happy number.

It is not an unprimeable number, because it can be changed into a prime (661663663) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 45571 + ... + 58309.

It is an arithmetic number, because the mean of its divisors is an integer number (22874670).

Almost surely, 2^661663660 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 661663660, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (823488120).

661663660 is an abundant number, since it is smaller than the sum of its proper divisors (985312580).

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

661663660 is a wasteful number, since it uses less digits than its factorization.

661663660 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12815 (or 12806 counting only the distinct ones).

The product of its (nonzero) digits is 139968, while the sum is 40.

The square root of 661663660 is about 25722.8237174693. The cubic root of 661663660 is about 871.3897109403.

The spelling of 661663660 in words is "six hundred sixty-one million, six hundred sixty-three thousand, six hundred sixty".