661561992 has 240 divisors, whose sum is σ = 2295786240. Its totient is φ = 174275712.

The previous prime is 661561981. The next prime is 661561997. The reversal of 661561992 is 299165166.

It is a happy number.

It is not an unprimeable number, because it can be changed into a prime (661561997) by changing a digit.

It is a polite number, since it can be written in 59 ways as a sum of consecutive naturals, for example, 766153 + ... + 767015.

It is an arithmetic number, because the mean of its divisors is an integer number (9565776).

Almost surely, 2^661561992 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 661561992, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1147893120).

661561992 is an abundant number, since it is smaller than the sum of its proper divisors (1634224248).

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

661561992 is a wasteful number, since it uses less digits than its factorization.

661561992 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 914 (or 888 counting only the distinct ones).

The product of its digits is 174960, while the sum is 45.

The square root of 661561992 is about 25720.8474199432. The cubic root of 661561992 is about 871.3450774946.

The spelling of 661561992 in words is "six hundred sixty-one million, five hundred sixty-one thousand, nine hundred ninety-two".