81217999 has 4 divisors (see below), whose sum is σ = 81237064. Its totient is φ = 81198936.

The previous prime is 81217987. The next prime is 81218041. The reversal of 81217999 is 99971218.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 81217999 - 2⁵ = 81217967 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81217919) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 109 + ... + 12745.

It is an arithmetic number, because the mean of its divisors is an integer number (20309266).

Almost surely, 2^81217999 is an apocalyptic number.

81217999 is a deficient number, since it is larger than the sum of its proper divisors (19065).

81217999 is a wasteful number, since it uses less digits than its factorization.

81217999 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19064.

The product of its digits is 81648, while the sum is 46.

The square root of 81217999 is about 9012.1029177434. The cubic root of 81217999 is about 433.0626826033.

The spelling of 81217999 in words is "eighty-one million, two hundred seventeen thousand, nine hundred ninety-nine".