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 A224335 #13 Jun 17 2017 02:59:46 %S A224335 60,212,508,996,1724,2740,4092,5828,7996,10644,13820,17572,21948, %T A224335 26996,32764,39300,46652,54868,63996,74084,85180,97332,110588,124996, %U A224335 140604,157460,175612,195108,215996,238324,262140,287492,314428,342996,373244 %N A224335 Number of idempotent 4X4 0..n matrices of rank 3. %C A224335 Row 4 of A224333. %H A224335 R. H. Hardin, <a href="/A224335/b224335.txt">Table of n, a(n) for n = 1..210</a> %H A224335 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (4,-6,4,-1). %F A224335 a(n) = 8*n^3 + 24*n^2 + 24*n + 4. %F A224335 a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4). - _Colin Barker_, Sep 20 2014 %F A224335 G.f.: -4*x*(x^3-5*x^2+7*x-15) / (x-1)^4. - _Colin Barker_, Sep 20 2014 %e A224335 Some solutions for n=3 %e A224335 ..1..0..0..0....1..0..0..0....1..0..0..0....1..0..0..3....1..0..0..0 %e A224335 ..0..1..0..0....2..0..1..1....0..1..1..0....0..1..0..2....0..1..0..0 %e A224335 ..3..2..0..0....0..0..1..0....0..0..0..0....0..0..1..1....1..2..0..1 %e A224335 ..0..0..0..1....0..0..0..1....0..0..2..1....0..0..0..0....0..0..0..1 %o A224335 (PARI) Vec(-4*x*(x^3-5*x^2+7*x-15)/(x-1)^4 + O(x^100)) \\ _Colin Barker_, Sep 20 2014 %K A224335 nonn,easy %O A224335 1,1 %A A224335 _R. H. Hardin_, formula via _M. F. Hasler_ _William J. Keith_ and _Rob Pratt_ in the Sequence Fans Mailing List, Apr 03 2013