81221504 has 128 divisors (see below), whose sum is σ = 210201600. Its totient is φ = 30357504.

The previous prime is 81221471. The next prime is 81221507. The reversal of 81221504 is 40512218.

It is a tau number, because it is divible by the number of its divisors (128).

It is a self number, because there is not a number n which added to its sum of digits gives 81221504.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81221507) 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 15 ways as a sum of consecutive naturals, for example, 221129 + ... + 221495.

It is an arithmetic number, because the mean of its divisors is an integer number (1642200).

Almost surely, 2^81221504 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 81221504, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (105100800).

81221504 is an abundant number, since it is smaller than the sum of its proper divisors (128980096).

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

81221504 is a wasteful number, since it uses less digits than its factorization.

81221504 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 420 (or 408 counting only the distinct ones).

The product of its (nonzero) digits is 640, while the sum is 23.

The square root of 81221504 is about 9012.2973763630. The cubic root of 81221504 is about 433.0689121866.

The spelling of 81221504 in words is "eighty-one million, two hundred twenty-one thousand, five hundred four".