641660665 has 16 divisors (see below), whose sum is σ = 830675088. Its totient is φ = 474013696.

The previous prime is 641660659. The next prime is 641660687. The reversal of 641660665 is 566066146.

It can be written as a sum of positive squares in 8 ways, for example, as 74839801 + 566820864 = 8651^2 + 23808^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-641660665 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 66712 + ... + 75721.

It is an arithmetic number, because the mean of its divisors is an integer number (51917193).

Almost surely, 2^641660665 is an apocalyptic number.

It is an amenable number.

641660665 is a deficient number, since it is larger than the sum of its proper divisors (189014423).

641660665 is a wasteful number, since it uses less digits than its factorization.

641660665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 142508.

The product of its (nonzero) digits is 155520, while the sum is 40.

The square root of 641660665 is about 25331.0217914714. The cubic root of 641660665 is about 862.5186060538.

It can be divided in two parts, 6416 and 60665, that added together give a square (67081 = 259²).

The spelling of 641660665 in words is "six hundred forty-one million, six hundred sixty thousand, six hundred sixty-five".