81305220 has 96 divisors (see below), whose sum is σ = 244339200. Its totient is φ = 20127744.

The previous prime is 81305197. The next prime is 81305221. The reversal of 81305220 is 2250318.

81305220 = T₄₈₄ + T₄₈₅ + ... + T₈₄₃.

It is a super-2 number, since 2×81305220² = 13221077598496800, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (81305221) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 80076 + ... + 81084.

It is an arithmetic number, because the mean of its divisors is an integer number (2545200).

Almost surely, 2^81305220 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 81305220, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (122169600).

81305220 is an abundant number, since it is smaller than the sum of its proper divisors (163033980).

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

81305220 is a wasteful number, since it uses less digits than its factorization.

81305220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1117 (or 1115 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 21.

The square root of 81305220 is about 9016.9407228838. The cubic root of 81305220 is about 433.2176509085.

Adding to 81305220 its reverse (2250318), we get a palindrome (83555538).

The spelling of 81305220 in words is "eighty-one million, three hundred five thousand, two hundred twenty".