81999321 has 16 divisors (see below), whose sum is σ = 113296320. Its totient is φ = 52719680.

The previous prime is 81999317. The next prime is 81999329. The reversal of 81999321 is 12399918.

It is a cyclic number.

It is not a de Polignac number, because 81999321 - 2² = 81999317 is a prime.

It is a super-2 number, since 2×81999321² = 13447777288922082, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (81999329) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5011 + ... + 13751.

It is an arithmetic number, because the mean of its divisors is an integer number (7081020).

Almost surely, 2^81999321 is an apocalyptic number.

It is an amenable number.

81999321 is a deficient number, since it is larger than the sum of its proper divisors (31296999).

81999321 is a wasteful number, since it uses less digits than its factorization.

81999321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8856.

The product of its digits is 34992, while the sum is 42.

The square root of 81999321 is about 9055.3476465567. The cubic root of 81999321 is about 434.4469494260.

The spelling of 81999321 in words is "eighty-one million, nine hundred ninety-nine thousand, three hundred twenty-one".