661191668 has 12 divisors (see below), whose sum is σ = 1160403300. Its totient is φ = 329647872.

The previous prime is 661191647. The next prime is 661191679. The reversal of 661191668 is 866191166.

It can be written as a sum of positive squares in 2 ways, for example, as 605061604 + 56130064 = 24598^2 + 7492^2 .

It is a hoax number, since the sum of its digits (44) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 235421 + ... + 238212.

It is an arithmetic number, because the mean of its divisors is an integer number (96700275).

Almost surely, 2^661191668 is an apocalyptic number.

It is an amenable number.

661191668 is a deficient number, since it is larger than the sum of its proper divisors (499211632).

661191668 is a wasteful number, since it uses less digits than its factorization.

661191668 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 473986 (or 473984 counting only the distinct ones).

The product of its digits is 93312, while the sum is 44.

The square root of 661191668 is about 25713.6475047785. The cubic root of 661191668 is about 871.1824622365.

The spelling of 661191668 in words is "six hundred sixty-one million, one hundred ninety-one thousand, six hundred sixty-eight".