19890991 has 2 divisors, whose sum is σ = 19890992. Its totient is φ = 19890990.

The previous prime is 19890973. The next prime is 19891007. The reversal of 19890991 is 19909891.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 19890991 - 2¹⁹ = 19366703 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (19890911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9945495 + 9945496.

It is an arithmetic number, because the mean of its divisors is an integer number (9945496).

Almost surely, 2^19890991 is an apocalyptic number.

19890991 is a deficient number, since it is larger than the sum of its proper divisors (1).

19890991 is an equidigital number, since it uses as much as digits as its factorization.

19890991 is an evil number, because the sum of its binary digits is even.

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

The square root of 19890991 is about 4459.9317259348. The cubic root of 19890991 is about 270.9477030388.

The spelling of 19890991 in words is "nineteen million, eight hundred ninety thousand, nine hundred ninety-one".