81217680 has 40 divisors (see below), whose sum is σ = 251775552. Its totient is φ = 21657984.

The previous prime is 81217673. The next prime is 81217691. The reversal of 81217680 is 8671218.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (40).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 168964 + ... + 169443.

Almost surely, 2^81217680 is an apocalyptic number.

81217680 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

81217680 is an abundant number, since it is smaller than the sum of its proper divisors (170557872).

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

81217680 is a wasteful number, since it uses less digits than its factorization.

81217680 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 338423 (or 338417 counting only the distinct ones).

The product of its (nonzero) digits is 5376, while the sum is 33.

The square root of 81217680 is about 9012.0852193041. The cubic root of 81217680 is about 433.0621156224.

Adding to 81217680 its reverse (8671218), we get a palindrome (89888898).

The spelling of 81217680 in words is "eighty-one million, two hundred seventeen thousand, six hundred eighty".