81217440 has 72 divisors (see below), whose sum is σ = 277159428. Its totient is φ = 21657600.

The previous prime is 81217417. The next prime is 81217441. The reversal of 81217440 is 4471218.

81217440 is a `hidden beast` number, since 8 + 1 + 217 + 440 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 81216144 + 1296 = 9012^2 + 36^2 .

It is a tau number, because it is divible by the number of its divisors (72).

It is not an unprimeable number, because it can be changed into a prime (81217441) 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, 26761 + ... + 29640.

Almost surely, 2^81217440 is an apocalyptic number.

81217440 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

81217440 is an abundant number, since it is smaller than the sum of its proper divisors (195941988).

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

81217440 is a wasteful number, since it uses less digits than its factorization.

81217440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 56422 (or 56411 counting only the distinct ones).

The product of its (nonzero) digits is 1792, while the sum is 27.

The square root of 81217440 is about 9012.0719038410. The cubic root of 81217440 is about 433.0616890526.

Adding to 81217440 its reverse (4471218), we get a palindrome (85688658).

The spelling of 81217440 in words is "eighty-one million, two hundred seventeen thousand, four hundred forty".