81518220 has 144 divisors (see below), whose sum is σ = 291852288. Its totient is φ = 18023040.

The previous prime is 81518219. The next prime is 81518221. The reversal of 81518220 is 2281518.

It is an interprime number because it is at equal distance from previous prime (81518219) and next prime (81518221).

It is not an unprimeable number, because it can be changed into a prime (81518221) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 38017 + ... + 40103.

It is an arithmetic number, because the mean of its divisors is an integer number (2026752).

Almost surely, 2^81518220 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 81518220, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (145926144).

81518220 is an abundant number, since it is smaller than the sum of its proper divisors (210334068).

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

81518220 is a wasteful number, since it uses less digits than its factorization.

81518220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2140 (or 2135 counting only the distinct ones).

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

The square root of 81518220 is about 9028.7440987105. The cubic root of 81518220 is about 433.5956294976.

Adding to 81518220 its reverse (2281518), we get a palindrome (83799738).

The spelling of 81518220 in words is "eighty-one million, five hundred eighteen thousand, two hundred twenty".