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 A274627 #9 Jul 06 2016 08:49:49
%S A274627 0,0,0,0,1,3,9,27,81,189,441,1029,2401,5145,11025,23625,50625,104625,
%T A274627 216225,446865,923521,1876833,3814209,7751457,15752961,31755969,
%U A274627 64016001,129048129,260144641,522337665,1048788225,2105834625,4228250625,8473082625,16979393025,34025371905,68184176641
%N A274627 Product_{i=0..3} (2^floor((n+i)/4)-1).
%C A274627 This is a four-dimensional analog of the holes-in-sheet-of-paper sequence A274230. See A274230 and A274626 for further information.
%D A274627 Tom Karzes, Posting to Math Fun Mailing List, Jul 05 2016.
%F A274627 Empirical g.f.: x^4*(1+2*x^2+6*x^3+4*x^4+8*x^6) / ((1-x)*(1-2*x)*(1-2*x^2)*(1+2*x^2)*(1-2*x^4)*(1-8*x^4)). - _Colin Barker_, Jul 06 2016
%p A274627 f:=(n,d) -> mul(2^floor((n+i)/d)-1, i = 0 .. d-1);
%p A274627 [seq(f(n,4),n=0..40)];
%o A274627 (PARI) a(n) = prod(i=0, 3, 2^floor((n+i)/4)-1) \\ _Colin Barker_, Jul 06 2016
%Y A274627 Cf. A274230, A274626.
%K A274627 nonn
%O A274627 0,6
%A A274627 _N. J. A. Sloane_, Jul 05 2016