81505240 has 32 divisors (see below), whose sum is σ = 183785760. Its totient is φ = 32531200.

The previous prime is 81505219. The next prime is 81505243. The reversal of 81505240 is 4250518.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81505243) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 18885 + ... + 22795.

It is an arithmetic number, because the mean of its divisors is an integer number (5743305).

Almost surely, 2^81505240 is an apocalyptic number.

It is an amenable number.

81505240 is an abundant number, since it is smaller than the sum of its proper divisors (102280520).

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

81505240 is a wasteful number, since it uses less digits than its factorization.

81505240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4443 (or 4439 counting only the distinct ones).

The product of its (nonzero) digits is 1600, while the sum is 25.

The square root of 81505240 is about 9028.0252547276. The cubic root of 81505240 is about 433.5726147245.

Adding to 81505240 its reverse (4250518), we get a palindrome (85755758).

The spelling of 81505240 in words is "eighty-one million, five hundred five thousand, two hundred forty".