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 A184880 #16 May 10 2024 16:51:55
%S A184880 1,1,2,-1,1,4,21,33,30,19,33,240,537,961,922,1223,2753,8380,17725,
%T A184880 27873,37494,57627,132577,300648,589953,942465,1460146,2566159,
%U A184880 5351297,11014388,20304613,34080673,57005646,105116835,207381921,402618208,728728425,1262355777,2218248522,4121995735,7892039233
%N A184880 Diagonal sums of number triangle A184879.
%H A184880 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (2,1,-6,7,8,-16)
%F A184880 G.f.: ( 1-x-x^2 ) / ( (4*x^3+3*x^2-x-1)*(4*x^3-5*x^2+3*x-1) )
%F A184880 a(n) = 2*a(n-1)+a(n-2)- 6*a(n-3)+7*a(n-4)+8*a(n-5)-16*a(n-6). [_Harvey P. Dale_, Sep 11 2011]
%t A184880 CoefficientList[Series[(1-x-x^2)/(1-2x-x^2+6x^3-7x^4-8x^5+16x^6),{x,0,50}], x] (* or *) LinearRecurrence[{2,1,-6,7,8,-16},{1,1,2,-1,1,4},50] (* _Harvey P. Dale_, Sep 11 2011 *)
%Y A184880 Cf. A184879.
%K A184880 sign,easy
%O A184880 0,3
%A A184880 _Paul Barry_, Jan 24 2011