81409 has 2 divisors, whose sum is σ = 81410. Its totient is φ = 81408.

The previous prime is 81401. The next prime is 81421. The reversal of 81409 is 90418.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 65025 + 16384 = 255^2 + 128^2 .

It is a cyclic number.

It is not a de Polignac number, because 81409 - 2³ = 81401 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81409.

It is not a weakly prime, because it can be changed into another prime (81401) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40704 + 40705.

It is an arithmetic number, because the mean of its divisors is an integer number (40705).

It is a Proth number, since it is equal to 159 ⋅ 2⁹ + 1 and 159 < 2⁹.

2⁸¹⁴⁰⁹ is an apocalyptic number.

It is an amenable number.

81409 is a deficient number, since it is larger than the sum of its proper divisors (1).

81409 is an equidigital number, since it uses as much as digits as its factorization.

81409 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 288, while the sum is 22.

The square root of 81409 is about 285.3226244096. The cubic root of 81409 is about 43.3401895792.

Subtracting 81409 from its reverse (90418), we obtain a palindrome (9009).

The spelling of 81409 in words is "eighty-one thousand, four hundred nine".