664691661 has 6 divisors (see below), whose sum is σ = 960110190. Its totient is φ = 443127768.

The previous prime is 664691659. The next prime is 664691663. The reversal of 664691661 is 166196466.

It is an interprime number because it is at equal distance from previous prime (664691659) and next prime (664691663).

It can be written as a sum of positive squares in only one way, i.e., 654387561 + 10304100 = 25581^2 + 3210^2 .

It is not a de Polignac number, because 664691661 - 2¹ = 664691659 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (664691663) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 36927306 + ... + 36927323.

It is an arithmetic number, because the mean of its divisors is an integer number (160018365).

Almost surely, 2^664691661 is an apocalyptic number.

It is an amenable number.

664691661 is a deficient number, since it is larger than the sum of its proper divisors (295418529).

664691661 is a wasteful number, since it uses less digits than its factorization.

664691661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 73854635 (or 73854632 counting only the distinct ones).

The product of its digits is 279936, while the sum is 45.

The square root of 664691661 is about 25781.6147865102. The cubic root of 664691661 is about 872.7169482651.

The spelling of 664691661 in words is "six hundred sixty-four million, six hundred ninety-one thousand, six hundred sixty-one".