661605655 has 4 divisors (see below), whose sum is σ = 793926792. Its totient is φ = 529284520.

The previous prime is 661605653. The next prime is 661605673. The reversal of 661605655 is 556506166.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 661605655 - 2¹ = 661605653 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661605653) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 66160561 + ... + 66160570.

It is an arithmetic number, because the mean of its divisors is an integer number (198481698).

Almost surely, 2^661605655 is an apocalyptic number.

661605655 is a deficient number, since it is larger than the sum of its proper divisors (132321137).

661605655 is a wasteful number, since it uses less digits than its factorization.

661605655 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 132321136.

The product of its (nonzero) digits is 162000, while the sum is 40.

The square root of 661605655 is about 25721.6961921254. The cubic root of 661605655 is about 871.3642466245.

The spelling of 661605655 in words is "six hundred sixty-one million, six hundred five thousand, six hundred fifty-five".