OFFSET
1,3
COMMENTS
First occurrences of n have ranks: 1, 3, 4, 8, 6, 7, 13, 11, 12, 18, ...
Second occurrences of n have ranks: 2, 5, 10, 14, 9, 20, ...
Triples of the form (a, b, a+b): (1,1,2), (3,2,5), (5,3,8), (7,4,11), (11,6,17), ... give sequence 2, 5, 8, 11, 17, ....
Every positive integer appears exactly twice. - Charlie Neder, Jan 12 2019
LINKS
Michael De Vlieger, Table of n, a(n) for n = 1..10000
FORMULA
MATHEMATICA
ekg[n_] := ekg[n] = Module[{ee, k},
If[n <= 2, n, ee = Array[ekg, n - 1];
For[k = 1, True, k++, If[FreeQ[ee, k] &&
GCD[ekg[n - 1], k] != 1, Return[k]]]]];
a[n_] := Quotient[ekg[n] - 1, 2] + 1;
Array[a, 68] (* Jean-François Alcover, Nov 21 2021 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul Curtz, Aug 31 2009
EXTENSIONS
More terms from Charlie Neder, Jan 12 2019
Name modified by Jean-François Alcover, Nov 23 2021
STATUS
approved