9781791661 has 16 divisors (see below), whose sum is σ = 10284120000. Its totient is φ = 9295308288.

The previous prime is 9781791629. The next prime is 9781791673. The reversal of 9781791661 is 1661971879.

It is a cyclic number.

It is not a de Polignac number, because 9781791661 - 2⁵ = 9781791629 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (9781791361) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 226215 + ... + 265963.

It is an arithmetic number, because the mean of its divisors is an integer number (642757500).

Almost surely, 2^9781791661 is an apocalyptic number.

It is an amenable number.

9781791661 is a deficient number, since it is larger than the sum of its proper divisors (502328339).

9781791661 is a wasteful number, since it uses less digits than its factorization.

9781791661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 39948.

The product of its digits is 1143072, while the sum is 55.

The square root of 9781791661 is about 98902.9406084571. The cubic root of 9781791661 is about 2138.6487860632.

The spelling of 9781791661 in words is "nine billion, seven hundred eighty-one million, seven hundred ninety-one thousand, six hundred sixty-one".