1991201491 has 2 divisors, whose sum is σ = 1991201492. Its totient is φ = 1991201490.

The previous prime is 1991201489. The next prime is 1991201521. The reversal of 1991201491 is 1941021991.

It is a weak prime.

It is an emirp because it is prime and its reverse (1941021991) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1991201491 - 2¹ = 1991201489 is a prime.

Together with 1991201489, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 1991201491.

It is not a weakly prime, because it can be changed into another prime (1991201791) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 995600745 + 995600746.

It is an arithmetic number, because the mean of its divisors is an integer number (995600746).

Almost surely, 2^1991201491 is an apocalyptic number.

1991201491 is a deficient number, since it is larger than the sum of its proper divisors (1).

1991201491 is an equidigital number, since it uses as much as digits as its factorization.

1991201491 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5832, while the sum is 37.

The square root of 1991201491 is about 44622.8808012212. The cubic root of 1991201491 is about 1258.0707628258.

The spelling of 1991201491 in words is "one billion, nine hundred ninety-one million, two hundred one thousand, four hundred ninety-one".