81191040 has 192 divisors, whose sum is σ = 301397760. Its totient is φ = 18536448.

The previous prime is 81191023. The next prime is 81191057. The reversal of 81191040 is 4019118.

It is an interprime number because it is at equal distance from previous prime (81191023) and next prime (81191057).

It is a tau number, because it is divible by the number of its divisors (192).

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a self number, because there is not a number n which added to its sum of digits gives 81191040.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 93649 + ... + 94511.

It is an arithmetic number, because the mean of its divisors is an integer number (1569780).

Almost surely, 2^81191040 is an apocalyptic number.

81191040 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81191040, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (150698880).

81191040 is an abundant number, since it is smaller than the sum of its proper divisors (220206720).

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

81191040 is a wasteful number, since it uses less digits than its factorization.

81191040 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 899 (or 880 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 24.

The square root of 81191040 is about 9010.6070827664. The cubic root of 81191040 is about 433.0147612517.

The spelling of 81191040 in words is "eighty-one million, one hundred ninety-one thousand, forty".