81609091 has 2 divisors, whose sum is σ = 81609092. Its totient is φ = 81609090.

The previous prime is 81609089. The next prime is 81609097. The reversal of 81609091 is 19090618.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81609091 - 2¹ = 81609089 is a prime.

Together with 81609089, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (81609097) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40804545 + 40804546.

It is an arithmetic number, because the mean of its divisors is an integer number (40804546).

Almost surely, 2^81609091 is an apocalyptic number.

81609091 is a deficient number, since it is larger than the sum of its proper divisors (1).

81609091 is an equidigital number, since it uses as much as digits as its factorization.

81609091 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3888, while the sum is 34.

The square root of 81609091 is about 9033.7750138024. The cubic root of 81609091 is about 433.7566840319.

The spelling of 81609091 in words is "eighty-one million, six hundred nine thousand, ninety-one".