661645640 has 64 divisors (see below), whose sum is σ = 1522326960. Its totient is φ = 258718720.

The previous prime is 661645639. The next prime is 661645651. The reversal of 661645640 is 46546166.

It can be written as a sum of positive squares in 8 ways, for example, as 520843684 + 140801956 = 22822^2 + 11866^2 .

It is a junction number, because it is equal to n+sod(n) for n = 661645594 and 661645603.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 976982 + ... + 977658.

Almost surely, 2^661645640 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 661645640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (761163480).

661645640 is an abundant number, since it is smaller than the sum of its proper divisors (860681320).

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

661645640 is a wasteful number, since it uses less digits than its factorization.

661645640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1202 (or 1198 counting only the distinct ones).

The product of its (nonzero) digits is 103680, while the sum is 38.

The square root of 661645640 is about 25722.4734424977. The cubic root of 661645640 is about 871.3818002821.

The spelling of 661645640 in words is "six hundred sixty-one million, six hundred forty-five thousand, six hundred forty".