1,1

A010888(a(n)) = A010888(n) and a(n)<>n;

a(a(n))=n: self-inverse permutation of the natural numbers.

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Index entries for sequences that are permutations of the natural numbers

a(n) = n + 9*(-1)^floor((n-1)/9).

(Haskell)

a100830 n = n + 9 * (-1) ^ ((n - 1) `div` 9)

-- Reinhard Zumkeller, Aug 01 2014

Sequence in context: A262412 A123895 A147519 * A180176 A168100 A088475

Adjacent sequences: A100827 A100828 A100829 * A100831 A100832 A100833

nonn,base

Reinhard Zumkeller, Jan 07 2005

approved