81491393 has 4 divisors (see below), whose sum is σ = 81627588. Its totient is φ = 81355200.

The previous prime is 81491381. The next prime is 81491413. The reversal of 81491393 is 39319418.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 76860289 + 4631104 = 8767^2 + 2152^2 .

It is a cyclic number.

It is not a de Polignac number, because 81491393 - 2¹⁰ = 81490369 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81491593) 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, 67196 + ... + 68397.

It is an arithmetic number, because the mean of its divisors is an integer number (20406897).

Almost surely, 2^81491393 is an apocalyptic number.

It is an amenable number.

81491393 is a deficient number, since it is larger than the sum of its proper divisors (136195).

81491393 is a wasteful number, since it uses less digits than its factorization.

81491393 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 136194.

The product of its digits is 23328, while the sum is 38.

The square root of 81491393 is about 9027.2583324064. The cubic root of 81491393 is about 433.5480599841.

The spelling of 81491393 in words is "eighty-one million, four hundred ninety-one thousand, three hundred ninety-three".