660921691 has 4 divisors (see below), whose sum is σ = 662455584. Its totient is φ = 659387800.

The previous prime is 660921689. The next prime is 660921749. The reversal of 660921691 is 196129066.

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 660921691 - 2¹ = 660921689 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (660921601) 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, 766300 + ... + 767161.

It is an arithmetic number, because the mean of its divisors is an integer number (165613896).

Almost surely, 2^660921691 is an apocalyptic number.

660921691 is a deficient number, since it is larger than the sum of its proper divisors (1533893).

660921691 is a wasteful number, since it uses less digits than its factorization.

660921691 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1533892.

The product of its (nonzero) digits is 34992, while the sum is 40.

The square root of 660921691 is about 25708.3972857119. The cubic root of 660921691 is about 871.0638726967.

The spelling of 660921691 in words is "six hundred sixty million, nine hundred twenty-one thousand, six hundred ninety-one".