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 A108870 #28 Dec 03 2023 18:39:09 %S A108870 1,4,9,20,46,103,233,525,1182,2660,5985,13467,30301,68178,153401, %T A108870 345152,776591,1747331,3931496,8845866,19903198,44782196,100759940, %U A108870 226709866,510097200,1147718700,2582367076,5810325920,13073233321,29414774973 %N A108870 a(n) = ceiling((9*(9/4)^n - 4) / 5). %C A108870 The old definition was "Tokuda's good set of increments for Shell sort", but that seems to be false. %C A108870 Adding 0, -1, -1, -1, ... to the terms gives A361506. For another version see A361507. %D A108870 N. Tokuda, An Improved Shellsort, IFIP Transactions, A-12 (1992) 449-457. %H A108870 Alois P. Heinz, <a href="/A108870/b108870.txt">Table of n, a(n) for n = 0..1000</a> %H A108870 Marcin Ciura, <a href="https://doi.org/10.1007/3-540-44669-9_12">Best Increments for the Average Case of Shellsort</a>, in R. Freivalds, (ed.), Fundamentals of Computation Theory: 13th International Symposium, FCT 2001, Riga, Latvia, August 2001, Lecture Notes in Computer Science, vol. 2138, Springer, pp. 106-117. %t A108870 A108870[n_]:=Ceiling[(9(9/4)^n-4)/5];Array[A108870,50,0] (* _Paolo Xausa_, Dec 02 2023 *) %Y A108870 Other sequences used for Shell sort: A003462, A033622, A036562, A036564, A036569, A055875, A055876, A361506, A361507. %K A108870 easy,nonn %O A108870 0,2 %A A108870 _Jud McCranie_, Jul 13 2005 %E A108870 Edited by _N. J. A. Sloane_, Mar 20 2023 at the suggestion of _Don Knuth_.