81687321 has 12 divisors (see below), whose sum is σ = 118087060. Its totient is φ = 54414720.

The previous prime is 81687301. The next prime is 81687323. The reversal of 81687321 is 12378618.

It can be written as a sum of positive squares in 2 ways, for example, as 80353296 + 1334025 = 8964^2 + 1155^2 .

It is not a de Polignac number, because 81687321 - 2⁹ = 81686809 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81687323) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 11661 + ... + 17301.

Almost surely, 2^81687321 is an apocalyptic number.

It is an amenable number.

81687321 is a deficient number, since it is larger than the sum of its proper divisors (36399739).

81687321 is a wasteful number, since it uses less digits than its factorization.

81687321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7256 (or 7253 counting only the distinct ones).

The product of its digits is 16128, while the sum is 36.

The square root of 81687321 is about 9038.1038387485. The cubic root of 81687321 is about 433.8952386470.

The spelling of 81687321 in words is "eighty-one million, six hundred eighty-seven thousand, three hundred twenty-one".