81581393 has 2 divisors, whose sum is σ = 81581394. Its totient is φ = 81581392.

The previous prime is 81581389. The next prime is 81581399. The reversal of 81581393 is 39318518.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 69422224 + 12159169 = 8332^2 + 3487^2 .

It is a cyclic number.

It is not a de Polignac number, because 81581393 - 2² = 81581389 is a prime.

It is not a weakly prime, because it can be changed into another prime (81581399) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40790696 + 40790697.

It is an arithmetic number, because the mean of its divisors is an integer number (40790697).

Almost surely, 2^81581393 is an apocalyptic number.

It is an amenable number.

81581393 is a deficient number, since it is larger than the sum of its proper divisors (1).

81581393 is an equidigital number, since it uses as much as digits as its factorization.

81581393 is an evil number, because the sum of its binary digits is even.

The product of its digits is 25920, while the sum is 38.

The square root of 81581393 is about 9032.2418590292. The cubic root of 81581393 is about 433.7076063620.

The spelling of 81581393 in words is "eighty-one million, five hundred eighty-one thousand, three hundred ninety-three".