660561491 has 4 divisors (see below), whose sum is σ = 664211184. Its totient is φ = 656911800.

The previous prime is 660561439. The next prime is 660561521. The reversal of 660561491 is 194165066.

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

It is a cyclic number.

It is not a de Polignac number, because 660561491 - 2¹⁴ = 660545107 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (660561191) by changing a digit.

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, 1824575 + ... + 1824936.

It is an arithmetic number, because the mean of its divisors is an integer number (166052796).

Almost surely, 2^660561491 is an apocalyptic number.

660561491 is a deficient number, since it is larger than the sum of its proper divisors (3649693).

660561491 is a wasteful number, since it uses less digits than its factorization.

660561491 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3649692.

The product of its (nonzero) digits is 38880, while the sum is 38.

The square root of 660561491 is about 25701.3908378516. The cubic root of 660561491 is about 870.9056016905.

The spelling of 660561491 in words is "six hundred sixty million, five hundred sixty-one thousand, four hundred ninety-one".