19981609 has 4 divisors (see below), whose sum is σ = 20670660. Its totient is φ = 19292560.

The previous prime is 19981567. The next prime is 19981649. The reversal of 19981609 is 90618991.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 17040384 + 2941225 = 4128^2 + 1715^2 .

It is a cyclic number.

It is not a de Polignac number, because 19981609 - 2²¹ = 17884457 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (19981649) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 344482 + ... + 344539.

It is an arithmetic number, because the mean of its divisors is an integer number (5167665).

Almost surely, 2^19981609 is an apocalyptic number.

It is an amenable number.

19981609 is a deficient number, since it is larger than the sum of its proper divisors (689051).

19981609 is an equidigital number, since it uses as much as digits as its factorization.

19981609 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 689050.

The product of its (nonzero) digits is 34992, while the sum is 43.

The square root of 19981609 is about 4470.0793057842. The cubic root of 19981609 is about 271.3585347199.

The spelling of 19981609 in words is "nineteen million, nine hundred eighty-one thousand, six hundred nine".