819961991 has 2 divisors, whose sum is σ = 819961992. Its totient is φ = 819961990.

The previous prime is 819961963. The next prime is 819962051. The reversal of 819961991 is 199169918.

819961991 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-819961991 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (819961591) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 409980995 + 409980996.

It is an arithmetic number, because the mean of its divisors is an integer number (409980996).

Almost surely, 2^819961991 is an apocalyptic number.

819961991 is a deficient number, since it is larger than the sum of its proper divisors (1).

819961991 is an equidigital number, since it uses as much as digits as its factorization.

819961991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 314928, while the sum is 53.

The square root of 819961991 is about 28634.9784529341. The cubic root of 819961991 is about 935.9757002817.

The spelling of 819961991 in words is "eight hundred nineteen million, nine hundred sixty-one thousand, nine hundred ninety-one".