81638583840 has 432 divisors, whose sum is σ = 311281123608. Its totient is φ = 19464192000.

The previous prime is 81638583821. The next prime is 81638583841. The reversal of 81638583840 is 4838583618.

81638583840 is a `hidden beast` number, since 8 + 16 + 3 + 8 + 583 + 8 + 40 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 50770904976 + 30867678864 = 225324^2 + 175692^2 .

It is a Smith number, since the sum of its digits (54) coincides with the sum of the digits of its prime factors.

It is not an unprimeable number, because it can be changed into a prime (81638583841) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 10624800 + ... + 10632480.

Almost surely, 2^81638583840 is an apocalyptic number.

81638583840 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 81638583840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (155640561804).

81638583840 is an abundant number, since it is smaller than the sum of its proper divisors (229642539768).

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

81638583840 is a wasteful number, since it uses less digits than its factorization.

81638583840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7785 (or 7763 counting only the distinct ones).

The product of its (nonzero) digits is 4423680, while the sum is 54.

The spelling of 81638583840 in words is "eighty-one billion, six hundred thirty-eight million, five hundred eighty-three thousand, eight hundred forty".