81331399 has 4 divisors (see below), whose sum is σ = 84135960. Its totient is φ = 78526840.

The previous prime is 81331379. The next prime is 81331403. The reversal of 81331399 is 99313318.

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 81331399 - 2²¹ = 79234247 is a prime.

It is a super-2 number, since 2×81331399² = 13229592926594402, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81331339) 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, 1402237 + ... + 1402294.

It is an arithmetic number, because the mean of its divisors is an integer number (21033990).

Almost surely, 2^81331399 is an apocalyptic number.

81331399 is a deficient number, since it is larger than the sum of its proper divisors (2804561).

81331399 is a wasteful number, since it uses less digits than its factorization.

81331399 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2804560.

The product of its digits is 17496, while the sum is 37.

The square root of 81331399 is about 9018.3922624823. The cubic root of 81331399 is about 433.2641423387.

The spelling of 81331399 in words is "eighty-one million, three hundred thirty-one thousand, three hundred ninety-nine".