81287891520 has 224 divisors, whose sum is σ = 296370938880. Its totient is φ = 18668943360.

The previous prime is 81287891491. The next prime is 81287891537. The reversal of 81287891520 is 2519878218.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 1932 + ... + 403211.

Almost surely, 2^81287891520 is an apocalyptic number.

81287891520 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 81287891520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (148185469440).

81287891520 is an abundant number, since it is smaller than the sum of its proper divisors (215083047360).

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

81287891520 is a wasteful number, since it uses less digits than its factorization.

81287891520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 405193 (or 405183 counting only the distinct ones).

The product of its (nonzero) digits is 645120, while the sum is 51.

The spelling of 81287891520 in words is "eighty-one billion, two hundred eighty-seven million, eight hundred ninety-one thousand, five hundred twenty".