1644791661 has 24 divisors (see below), whose sum is σ = 2407781376. Its totient is φ = 1081809600.

The previous prime is 1644791657. The next prime is 1644791669. The reversal of 1644791661 is 1661974461.

1644791661 is a `hidden beast` number, since 16 + 4 + 479 + 166 + 1 = 666.

It is not a de Polignac number, because 1644791661 - 2² = 1644791657 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1644791669) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 858841 + ... + 860753.

It is an arithmetic number, because the mean of its divisors is an integer number (100324224).

Almost surely, 2^1644791661 is an apocalyptic number.

It is an amenable number.

1644791661 is a deficient number, since it is larger than the sum of its proper divisors (762989715).

1644791661 is a wasteful number, since it uses less digits than its factorization.

1644791661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3153 (or 3150 counting only the distinct ones).

The product of its digits is 217728, while the sum is 45.

The square root of 1644791661 is about 40556.0311297839. The cubic root of 1644791661 is about 1180.4211034147.

The spelling of 1644791661 in words is "one billion, six hundred forty-four million, seven hundred ninety-one thousand, six hundred sixty-one".