661978656 has 120 divisors (see below), whose sum is σ = 1956732624. Its totient is φ = 220449600.

The previous prime is 661978651. The next prime is 661978699. The reversal of 661978656 is 656879166.

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

It is not an unprimeable number, because it can be changed into a prime (661978651) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 629331 + ... + 630381.

Almost surely, 2^661978656 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 661978656, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (978366312).

661978656 is an abundant number, since it is smaller than the sum of its proper divisors (1294753968).

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

661978656 is an frugal number, since it uses more digits than its factorization.

661978656 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1088 (or 1056 counting only the distinct ones).

The product of its digits is 3265920, while the sum is 54.

The square root of 661978656 is about 25728.9458781350. The cubic root of 661978656 is about 871.5279688619.

The spelling of 661978656 in words is "six hundred sixty-one million, nine hundred seventy-eight thousand, six hundred fifty-six".