81991098 has 48 divisors (see below), whose sum is σ = 205620480. Its totient is φ = 23126688.

The previous prime is 81991097. The next prime is 81991121. The reversal of 81991098 is 89019918.

It is not an unprimeable number, because it can be changed into a prime (81991097) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 5836 + ... + 14072.

It is an arithmetic number, because the mean of its divisors is an integer number (4283760).

Almost surely, 2^81991098 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81991098, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (102810240).

81991098 is an abundant number, since it is smaller than the sum of its proper divisors (123629382).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81991098 is a wasteful number, since it uses less digits than its factorization.

81991098 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8331 (or 8328 counting only the distinct ones).

The product of its (nonzero) digits is 46656, while the sum is 45.

The square root of 81991098 is about 9054.8935940739. The cubic root of 81991098 is about 434.4324266363.

The spelling of 81991098 in words is "eighty-one million, nine hundred ninety-one thousand, ninety-eight".