661865904 has 240 divisors, whose sum is σ = 2229357312. Its totient is φ = 186188544.

The previous prime is 661865899. The next prime is 661865909. The reversal of 661865904 is 409568166.

661865904 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is an interprime number because it is at equal distance from previous prime (661865899) and next prime (661865909).

It is a self number, because there is not a number n which added to its sum of digits gives 661865904.

It is not an unprimeable number, because it can be changed into a prime (661865909) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 2258782 + ... + 2259074.

Almost surely, 2^661865904 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 661865904, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1114678656).

661865904 is an abundant number, since it is smaller than the sum of its proper divisors (1567491408).

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

661865904 is a wasteful number, since it uses less digits than its factorization.

661865904 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 406 (or 388 counting only the distinct ones).

The product of its (nonzero) digits is 311040, while the sum is 45.

The square root of 661865904 is about 25726.7546340381. The cubic root of 661865904 is about 871.4784848389.

The spelling of 661865904 in words is "six hundred sixty-one million, eight hundred sixty-five thousand, nine hundred four".