81563999 has 4 divisors (see below), whose sum is σ = 88978920. Its totient is φ = 74149080.

The previous prime is 81563987. The next prime is 81564001. The reversal of 81563999 is 99936518.

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 81563999 - 2⁴ = 81563983 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 (81563929) 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, 3707444 + ... + 3707465.

It is an arithmetic number, because the mean of its divisors is an integer number (22244730).

Almost surely, 2^81563999 is an apocalyptic number.

81563999 is a deficient number, since it is larger than the sum of its proper divisors (7414921).

81563999 is a wasteful number, since it uses less digits than its factorization.

81563999 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7414920.

The product of its digits is 524880, while the sum is 50.

The square root of 81563999 is about 9031.2789238291. The cubic root of 81563999 is about 433.6767805162.

The spelling of 81563999 in words is "eighty-one million, five hundred sixty-three thousand, nine hundred ninety-nine".