OFFSET

1,2

COMMENTS

This is a permutation of the positive integers.

1, 2, 6, 9, 15, 19, ... are in a(n) and A064664(n).

LINKS

Jean-François Alcover, Table of n, a(n) for n = 1..1000

Jean-François Alcover, Plot of a(1..1000)

FORMULA

Interleave the occurrences in A164912.

MATHEMATICA

nmax = 120;

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]]]]];

b[n_] := Quotient[ekg[n] - 1, 2] + 1;

bb = Array[b, nmax];

TakeWhile[Table[Position[bb, n], {n, 1, nmax}], Length[#] == 2&] // Flatten (* Jean-François Alcover, Nov 21 2021 *)

CROSSREFS

KEYWORD

nonn

AUTHOR

Paul Curtz, Nov 21 2021

STATUS

approved