661971655 has 4 divisors (see below), whose sum is σ = 794365992. Its totient is φ = 529577320.

The previous prime is 661971649. The next prime is 661971727. The reversal of 661971655 is 556179166.

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

It is a de Polignac number, because none of the positive numbers 2^k-661971655 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 66197161 + ... + 66197170.

It is an arithmetic number, because the mean of its divisors is an integer number (198591498).

Almost surely, 2^661971655 is an apocalyptic number.

661971655 is a deficient number, since it is larger than the sum of its proper divisors (132394337).

661971655 is a wasteful number, since it uses less digits than its factorization.

661971655 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 132394336.

The product of its digits is 340200, while the sum is 46.

The square root of 661971655 is about 25728.8098247859. The cubic root of 661971655 is about 871.5248964624.

The spelling of 661971655 in words is "six hundred sixty-one million, nine hundred seventy-one thousand, six hundred fifty-five".