19987091 has 2 divisors, whose sum is σ = 19987092. Its totient is φ = 19987090.

The previous prime is 19987081. The next prime is 19987109. The reversal of 19987091 is 19078991.

Together with next prime (19987109) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It is an emirp because it is prime and its reverse (19078991) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 19987091 - 2⁶ = 19987027 is a prime.

It is a Sophie Germain prime.

It is not a weakly prime, because it can be changed into another prime (19987001) 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, 9993545 + 9993546.

It is an arithmetic number, because the mean of its divisors is an integer number (9993546).

Almost surely, 2^19987091 is an apocalyptic number.

19987091 is a deficient number, since it is larger than the sum of its proper divisors (1).

19987091 is an equidigital number, since it uses as much as digits as its factorization.

19987091 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 19987091 is about 4470.6924519586. The cubic root of 19987091 is about 271.3833483951.

The spelling of 19987091 in words is "nineteen million, nine hundred eighty-seven thousand, ninety-one".