19987109 has 2 divisors, whose sum is σ = 19987110. Its totient is φ = 19987108.

The previous prime is 19987091. The next prime is 19987117. The reversal of 19987109 is 90178991.

Together with previous prime (19987091) it forms an Ormiston pair, because they use the same digits, order apart.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15484225 + 4502884 = 3935^2 + 2122^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-19987109 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 19987109.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (19987129) 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 as a sum of consecutive naturals, namely, 9993554 + 9993555.

It is an arithmetic number, because the mean of its divisors is an integer number (9993555).

Almost surely, 2^19987109 is an apocalyptic number.

It is an amenable number.

19987109 is a deficient number, since it is larger than the sum of its proper divisors (1).

19987109 is an equidigital number, since it uses as much as digits as its factorization.

19987109 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 40824, while the sum is 44.

The square root of 19987109 is about 4470.6944650692. The cubic root of 19987109 is about 271.3834298626.

The spelling of 19987109 in words is "nineteen million, nine hundred eighty-seven thousand, one hundred nine".