19665661 has 4 divisors (see below), whose sum is σ = 19720800. Its totient is φ = 19610524.

The previous prime is 19665647. The next prime is 19665673. The reversal of 19665661 is 16656691.

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.

It is a cyclic number.

It is not a de Polignac number, because 19665661 - 2²³ = 11277053 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 (19665601) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 27031 + ... + 27748.

It is an arithmetic number, because the mean of its divisors is an integer number (4930200).

Almost surely, 2^19665661 is an apocalyptic number.

It is an amenable number.

19665661 is a deficient number, since it is larger than the sum of its proper divisors (55139).

19665661 is an equidigital number, since it uses as much as digits as its factorization.

19665661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 55138.

The product of its digits is 58320, while the sum is 40.

The square root of 19665661 is about 4434.5981779638. The cubic root of 19665661 is about 269.9206945868.

The spelling of 19665661 in words is "nineteen million, six hundred sixty-five thousand, six hundred sixty-one".