81343721 has 4 divisors (see below), whose sum is σ = 83967744. Its totient is φ = 78719700.

The previous prime is 81343697. The next prime is 81343733. The reversal of 81343721 is 12734318.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81343721 is a prime.

It is a super-2 number, since 2×81343721² = 13233601892251682, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81343771) 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, 1311965 + ... + 1312026.

It is an arithmetic number, because the mean of its divisors is an integer number (20991936).

Almost surely, 2^81343721 is an apocalyptic number.

It is an amenable number.

81343721 is a deficient number, since it is larger than the sum of its proper divisors (2624023).

81343721 is a wasteful number, since it uses less digits than its factorization.

81343721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2624022.

The product of its digits is 4032, while the sum is 29.

The square root of 81343721 is about 9019.0753960703. The cubic root of 81343721 is about 433.2860215934.

The spelling of 81343721 in words is "eighty-one million, three hundred forty-three thousand, seven hundred twenty-one".