81521280 has 96 divisors (see below), whose sum is σ = 281523060. Its totient is φ = 21737472.

The previous prime is 81521213. The next prime is 81521281. The reversal of 81521280 is 8212518.

It can be written as a sum of positive squares in 2 ways, for example, as 80138304 + 1382976 = 8952^2 + 1176^2 .

It is a tau number, because it is divible by the number of its divisors (96).

It is not an unprimeable number, because it can be changed into a prime (81521281) 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 11 ways as a sum of consecutive naturals, for example, 1317 + ... + 12836.

Almost surely, 2^81521280 is an apocalyptic number.

81521280 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 81521280, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (140761530).

81521280 is an abundant number, since it is smaller than the sum of its proper divisors (200001780).

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

81521280 is a wasteful number, since it uses less digits than its factorization.

81521280 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14178 (or 14163 counting only the distinct ones).

The product of its (nonzero) digits is 1280, while the sum is 27.

The square root of 81521280 is about 9028.9135559047. The cubic root of 81521280 is about 433.6010548124.

Adding to 81521280 its reverse (8212518), we get a palindrome (89733798).

The spelling of 81521280 in words is "eighty-one million, five hundred twenty-one thousand, two hundred eighty".