19809991 has 2 divisors, whose sum is σ = 19809992. Its totient is φ = 19809990.

The previous prime is 19809973. The next prime is 19810001. The reversal of 19809991 is 19990891.

It is a strong prime.

It is an emirp because it is prime and its reverse (19990891) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 19809991 - 2⁹ = 19809479 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (19809941) 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, 9904995 + 9904996.

It is an arithmetic number, because the mean of its divisors is an integer number (9904996).

Almost surely, 2^19809991 is an apocalyptic number.

19809991 is a deficient number, since it is larger than the sum of its proper divisors (1).

19809991 is an equidigital number, since it uses as much as digits as its factorization.

19809991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 52488, while the sum is 46.

The square root of 19809991 is about 4450.8416058090. The cubic root of 19809991 is about 270.5794186895.

The spelling of 19809991 in words is "nineteen million, eight hundred nine thousand, nine hundred ninety-one".