81643856 has 40 divisors (see below), whose sum is σ = 182410944. Its totient is φ = 34675200.

The previous prime is 81643853. The next prime is 81643897. The reversal of 81643856 is 65834618.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81643853) 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 7 ways as a sum of consecutive naturals, for example, 9431 + ... + 15881.

Almost surely, 2^81643856 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81643856, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (91205472).

81643856 is an abundant number, since it is smaller than the sum of its proper divisors (100767088).

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

81643856 is a wasteful number, since it uses less digits than its factorization.

81643856 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6579 (or 6573 counting only the distinct ones).

The product of its digits is 138240, while the sum is 41.

The square root of 81643856 is about 9035.6989768363. The cubic root of 81643856 is about 433.8182678995.

The spelling of 81643856 in words is "eighty-one million, six hundred forty-three thousand, eight hundred fifty-six".