81581965920 has 1728 divisors, whose sum is σ = 381471068160. Its totient is φ = 15676416000.

The previous prime is 81581965909. The next prime is 81581965943. The reversal of 81581965920 is 2956918518.

81581965920 is a `hidden beast` number, since 8 + 1 + 581 + 9 + 6 + 59 + 2 + 0 = 666.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 287 ways as a sum of consecutive naturals, for example, 540277845 + ... + 540277995.

It is an arithmetic number, because the mean of its divisors is an integer number (220758720).

Almost surely, 2^81581965920 is an apocalyptic number.

81581965920 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 81581965920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (190735534080).

81581965920 is an abundant number, since it is smaller than the sum of its proper divisors (299889102240).

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

81581965920 is a wasteful number, since it uses less digits than its factorization.

81581965920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 249 (or 231 counting only the distinct ones).

The product of its (nonzero) digits is 1555200, while the sum is 54.

The spelling of 81581965920 in words is "eighty-one billion, five hundred eighty-one million, nine hundred sixty-five thousand, nine hundred twenty".