81555643680 has 384 divisors, whose sum is σ = 300058214400. Its totient is φ = 18235736064.

The previous prime is 81555643661. The next prime is 81555643691. The reversal of 81555643680 is 8634655518.

It is a happy number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 29993361 + ... + 29996079.

It is an arithmetic number, because the mean of its divisors is an integer number (781401600).

Almost surely, 2^81555643680 is an apocalyptic number.

81555643680 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 81555643680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (150029107200).

81555643680 is an abundant number, since it is smaller than the sum of its proper divisors (218502570720).

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

81555643680 is a wasteful number, since it uses less digits than its factorization.

81555643680 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2936 (or 2928 counting only the distinct ones).

The product of its (nonzero) digits is 3456000, while the sum is 51.

The spelling of 81555643680 in words is "eighty-one billion, five hundred fifty-five million, six hundred forty-three thousand, six hundred eighty".