81440432640 has 800 divisors, whose sum is σ = 351028782720. Its totient is φ = 17629249536.

The previous prime is 81440432581. The next prime is 81440432653. The reversal of 81440432640 is 4623404418.

81440432640 is a `hidden beast` number, since 8 + 1 + 4 + 4 + 0 + 4 + 3 + 2 + 640 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 81440432595 and 81440432604.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 79 ways as a sum of consecutive naturals, for example, 27577404 + ... + 27580356.

Almost surely, 2^81440432640 is an apocalyptic number.

81440432640 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 81440432640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (175514391360).

81440432640 is an abundant number, since it is smaller than the sum of its proper divisors (269588350080).

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

81440432640 is a wasteful number, since it uses less digits than its factorization.

81440432640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3014 (or 2989 counting only the distinct ones).

The product of its (nonzero) digits is 73728, while the sum is 36.

The spelling of 81440432640 in words is "eighty-one billion, four hundred forty million, four hundred thirty-two thousand, six hundred forty".