81900090091 has 2 divisors, whose sum is σ = 81900090092. Its totient is φ = 81900090090.

The previous prime is 81900090089. The next prime is 81900090101. The reversal of 81900090091 is 19009000918.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81900090091 - 2¹ = 81900090089 is a prime.

Together with 81900090089, 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 81900090091.

It is not a weakly prime, because it can be changed into another prime (81900090031) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40950045045 + 40950045046.

It is an arithmetic number, because the mean of its divisors is an integer number (40950045046).

Almost surely, 2^81900090091 is an apocalyptic number.

81900090091 is a deficient number, since it is larger than the sum of its proper divisors (1).

81900090091 is an equidigital number, since it uses as much as digits as its factorization.

81900090091 is an evil number, because the sum of its binary digits is even.

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

The spelling of 81900090091 in words is "eighty-one billion, nine hundred million, ninety thousand, ninety-one".