661565620 has 24 divisors (see below), whose sum is σ = 1390191264. Its totient is φ = 264454176.

The previous prime is 661565609. The next prime is 661565651. The reversal of 661565620 is 26565166.

It is a self number, because there is not a number n which added to its sum of digits gives 661565620.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 23419 + ... + 43261.

It is an arithmetic number, because the mean of its divisors is an integer number (57924636).

Almost surely, 2^661565620 is an apocalyptic number.

It is an amenable number.

661565620 is an abundant number, since it is smaller than the sum of its proper divisors (728625644).

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

661565620 is a wasteful number, since it uses less digits than its factorization.

661565620 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21519 (or 21517 counting only the distinct ones).

The product of its (nonzero) digits is 64800, while the sum is 37.

The square root of 661565620 is about 25720.9179462942. The cubic root of 661565620 is about 871.3466703079.

The spelling of 661565620 in words is "six hundred sixty-one million, five hundred sixty-five thousand, six hundred twenty".