A084933 - OEIS

%I #24 Nov 05 2014 13:12:08

%S 1,2,3,5,4,11,6,8,7,14,9,26,10,20,18,17,12,29,13,32,15,23,16,56,21,35,

%T 22,38,19,59,24,41,33,47,25,62,27,44,39,53,28,95,30,50,36,65,31,92,34,

%U 74,42,68,37,98,40,71,49,77,43,101,45,80,46,83,48,137,51,86,52

%N Inverse of A084937.

%C Empirically, A084937 is a permutation of the natural numbers. Assuming that is true, we will have a(A084937(n)) = A084937(a(n)) = n. (Comment revised by _N. J. A. Sloane_, Nov 05 2014)

%H Reinhard Zumkeller, <a href="/A084933/b084933.txt">Table of n, a(n) for n = 1..10000</a>

%H <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a>

%t f[s_] := Block[{k = 1, l = Take[s, -2]}, While[ Union[ GCD[k, l]] != {1} || MemberQ[s, k], k++]; Append[s, k]]; Ordering@ Nest[f, {1, 2}, 100] (* _Robert G. Wilson v_, Jun 26 2011 *)

%o (Haskell)

%o import Data.List (elemIndex)

%o import Data.Maybe (fromJust)

%o a084933 n = (fromJust $ elemIndex n a084937_list) + 1

%o -- _Reinhard Zumkeller_, Jan 28 2012

%Y Cf. A084937. For records see A249684, A249685.

%K nonn

%O 1,2

%A _Reinhard Zumkeller_, Jun 13 2003