660991 has 6 divisors (see below), whose sum is σ = 697992. Its totient is φ = 625860.

The previous prime is 660983. The next prime is 661009. The reversal of 660991 is 199066.

It is not a de Polignac number, because 660991 - 2³ = 660983 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 (660901) by changing a digit.

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 5 ways as a sum of consecutive naturals, for example, 555 + ... + 1276.

It is an arithmetic number, because the mean of its divisors is an integer number (116332).

2⁶⁶⁰⁹⁹¹ is an apocalyptic number.

660991 is a deficient number, since it is larger than the sum of its proper divisors (37001).

660991 is a wasteful number, since it uses less digits than its factorization.

660991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1869 (or 1850 counting only the distinct ones).

The product of its (nonzero) digits is 2916, while the sum is 31.

The square root of 660991 is about 813.0135300227. The cubic root of 660991 is about 87.1094320306.

The spelling of 660991 in words is "six hundred sixty thousand, nine hundred ninety-one".