81789991 has 2 divisors, whose sum is σ = 81789992. Its totient is φ = 81789990.

The previous prime is 81789949. The next prime is 81790013. The reversal of 81789991 is 19998718.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81789991 - 2²¹ = 79692839 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81789691) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40894995 + 40894996.

It is an arithmetic number, because the mean of its divisors is an integer number (40894996).

Almost surely, 2^81789991 is an apocalyptic number.

81789991 is a deficient number, since it is larger than the sum of its proper divisors (1).

81789991 is an equidigital number, since it uses as much as digits as its factorization.

81789991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 326592, while the sum is 52.

The square root of 81789991 is about 9043.7818969721. The cubic root of 81789991 is about 434.0769452366.

The spelling of 81789991 in words is "eighty-one million, seven hundred eighty-nine thousand, nine hundred ninety-one".