19791661 has 4 divisors (see below), whose sum is σ = 20652192. Its totient is φ = 18931132.

The previous prime is 19791649. The next prime is 19791691. The reversal of 19791661 is 16619791.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 16619791 = 431 ⋅38561.

It is a cyclic number.

It is not a de Polignac number, because 19791661 - 2⁷ = 19791533 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 (19791691) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 430231 + ... + 430276.

It is an arithmetic number, because the mean of its divisors is an integer number (5163048).

Almost surely, 2^19791661 is an apocalyptic number.

It is an amenable number.

19791661 is a deficient number, since it is larger than the sum of its proper divisors (860531).

19791661 is an equidigital number, since it uses as much as digits as its factorization.

19791661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 860530.

The product of its digits is 20412, while the sum is 40.

The square root of 19791661 is about 4448.7819681346. The cubic root of 19791661 is about 270.4959380650.

The spelling of 19791661 in words is "nineteen million, seven hundred ninety-one thousand, six hundred sixty-one".