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 A285507 #18 May 14 2017 00:10:33 %S A285507 1,1,2,2,3,3,3,3,4,4,5,5,5,5,6,6,8,8,8,8,8,8,8,9,9,11,11,12,12,13,13, %T A285507 13,13,13,13,13,13,14,14,16,16,17,17,17,17,18,18,21,21,21,20,21,21,21, %U A285507 21,21,21,21,21,22,22,24,24,24,24,24,25,25,26,26,26,26,27,27,32,32,34,30,31,29,34,33,34,34,33,33,34,34 %N A285507 a(1) = a(2) = 1, a(3) = a(4) = 2; a(n) = a(a(n-2)-1) + a(n-a(n-3)-1) for n > 4. %H A285507 Altug Alkan, <a href="/A285507/b285507.txt">Table of n, a(n) for n = 1..10000</a> %H A285507 Altug Alkan, <a href="/A285507/a285507.png">Alternative scatterplot of A285507</a> %e A285507 a(5) = 3 because a(5) = a(a(3)-1) + a(5-a(2)-1) = a(1) + a(3) = 3. %t A285507 a[1]=a[2]=1; a[3]=a[4]=2; a[n_] := a[n] = a[a[n-2]-1] + a[n-a[n-3]-1]; Array[a, 88] (* _Giovanni Resta_, Apr 21 2017 *) %o A285507 (PARI) a=vector(10000); a[1]=a[2]=1; a[3]=a[4]=2; for(n=5, #a, a[n]=a[a[n-2]-1]+a[n-a[n-3]-1]); va = vector(10000, n, a[n]) %Y A285507 Cf. A005185, A055748, A284523. %K A285507 nonn,look %O A285507 1,3 %A A285507 _Altug Alkan_, Apr 20 2017