This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A107039 #20 Feb 25 2024 01:44:25
%S A107039 1,1,1,1,1,1,1,2,1,1,1,1,1,1,1,2,2,1,1,1,1,1,2,1,1,1,1,1,1,1,2,1,1,2,
%T A107039 2,1,2,1,1,1,1,1,1,1,3,1,1,1,2,1,2,1,1,1,1,1,1,1,2,1,1,1,1,1,1,3,1,2,
%U A107039 1,1,1,1,2,1,1,1,1,1,1,1,3,1,1,1,1,1,1,2,2,1,1,1,1,1,2,1,2,1,1,1,1,2,1,1,1
%N A107039 First differences of indices of squarefree Jacobsthal numbers.
%C A107039 First differences of A107037.
%H A107039 Amiram Eldar, <a href="/A107039/b107039.txt">Table of n, a(n) for n = 1..898</a>
%p A107039 A001045 := proc(n) option remember : if n <= 1 then n; else A001045(n-1)+2*A001045(n-2) ; fi ; end: A107037 := proc(nmax) local a,n; a := [] ; n := 1: while nops(a) < nmax do if numtheory[issqrfree]( A001045(n) ) then a := [op(a),n] ; fi ; n := n+1: od : RETURN(a) ; end: A107039 := proc(nmax) local a107037 ; a107037 := A107037(nmax+1) : [seq( a107037[i]-a107037[i-1],i=2..nmax)] ; end: op(A107039(120)) ; # _R. J. Mathar_, Aug 12 2007
%t A107039 Position[LinearRecurrence[{1, 2}, {0, 1}, 131], _?SquareFreeQ]-1 // Rest // Flatten // Differences (* _Jean-François Alcover_, Dec 09 2023 *)
%Y A107039 Cf. A001045, A005117, A107037.
%K A107039 nonn
%O A107039 1,8
%A A107039 _Paul Barry_, May 09 2005
%E A107039 More terms from _R. J. Mathar_, Aug 12 2007
%E A107039 Offset corrected by _Amiram Eldar_, Feb 25 2024