661911920 has 20 divisors (see below), whose sum is σ = 1538945400. Its totient is φ = 264764736.

The previous prime is 661911893. The next prime is 661911941. The reversal of 661911920 is 29119166.

It is a tau number, because it is divible by the number of its divisors (20).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4136870 + ... + 4137029.

It is an arithmetic number, because the mean of its divisors is an integer number (76947270).

Almost surely, 2^661911920 is an apocalyptic number.

It is an amenable number.

661911920 is an abundant number, since it is smaller than the sum of its proper divisors (877033480).

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

661911920 is a wasteful number, since it uses less digits than its factorization.

661911920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8273912 (or 8273906 counting only the distinct ones).

The product of its (nonzero) digits is 5832, while the sum is 35.

The square root of 661911920 is about 25727.6489403910. The cubic root of 661911920 is about 871.4986807851.

The spelling of 661911920 in words is "six hundred sixty-one million, nine hundred eleven thousand, nine hundred twenty".