661555220 has 12 divisors (see below), whose sum is σ = 1389266004. Its totient is φ = 264622080.

The previous prime is 661555217. The next prime is 661555241. The reversal of 661555220 is 22555166.

It can be written as a sum of positive squares in 2 ways, for example, as 267453316 + 394101904 = 16354^2 + 19852^2 .

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 16538861 + ... + 16538900.

It is an arithmetic number, because the mean of its divisors is an integer number (115772167).

Almost surely, 2^661555220 is an apocalyptic number.

It is an amenable number.

661555220 is an abundant number, since it is smaller than the sum of its proper divisors (727710784).

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

661555220 is a wasteful number, since it uses less digits than its factorization.

661555220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 33077770 (or 33077768 counting only the distinct ones).

The product of its (nonzero) digits is 18000, while the sum is 32.

The square root of 661555220 is about 25720.7157754212. The cubic root of 661555220 is about 871.3421043447.

The spelling of 661555220 in words is "six hundred sixty-one million, five hundred fifty-five thousand, two hundred twenty".