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 A090667 #21 May 04 2024 00:44:43
%S A090667 1,1,13,149,1490,13624,117920,987568,8111200,65866496,531372800,
%T A090667 4270866688,34254920192,274425014272,2197077311488,17583865032704,
%U A090667 140702055981056,1125749585477632,9006563605151744,72054913990721536,576449482336632832,4611638739487686656
%N A090667 Number of compositions of 3n with each part less than or equal to n.
%H A090667 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (22,-188,808,-1856,2176,-1024).
%F A090667 a(n) = 2^(3n-1)-(2n+1)*2^(2n-2)+(n+2)*(n-1)*2^(n-4), n>0.
%F A090667 G.f.: (896*x^6-1968*x^5+1704*x^4-757*x^3+179*x^2-21*x+1) / ((2*x-1)^3*(4*x-1)^2*(8*x-1)). - _Colin Barker_, May 15 2013
%e A090667 a(2)=13 since there is one composition of 6 of the form 1+1+1+1+1+1, five of the form 2+1+1+1+1, six of the form 2+2+1+1 and one of the form 2+2+2 and 1+5+6+1=13.
%p A090667 A090667:=n->`if`(n=0,1,2^(3*n-1)-(2*n+1)*2^(2*n-2)+(n+2)*(n-1)*2^(n-4)); seq(A090667(n), n=0..50); # _Wesley Ivan Hurt_, Nov 14 2013
%t A090667 LinearRecurrence[{22,-188,808,-1856,2176,-1024},{1,1,13,149,1490,13624,117920},30] (* _Harvey P. Dale_, May 04 2024 *)
%Y A090667 Cf. A008464.
%K A090667 nonn,easy
%O A090667 0,3
%A A090667 _Henry Bottomley_, Dec 16 2003
%E A090667 More terms from _Colin Barker_, May 15 2013