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 A224327 #16 Aug 29 2018 08:46:02 %S A224327 1,10,51,212,805,2910,10199,34984,118089,393650,1299067,4251516, %T A224327 13817453,44641030,143489055,459165008,1463588497,4649045850, %U A224327 14721978563,46490458660,146444944821,460255540910,1443528741991,4518872583672 %N A224327 Number of idempotent n X n 0..2 matrices of rank n-1. %C A224327 Column 2 of A224333. %H A224327 R. H. Hardin, <a href="/A224327/b224327.txt">Table of n, a(n) for n = 1..210</a> %H A224327 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (8,-22,24,-9). %F A224327 a(n) = n*(2*3^(n-1)-1). %F A224327 a(n) = 8*a(n-1) - 22*a(n-2) + 24*a(n-3) - 9*a(n-4). %F A224327 G.f.: x*(1 + 2*x - 7*x^2) / ((1 - x)^2*(1 - 3*x)^2). - _Colin Barker_, Aug 29 2018 %e A224327 Some solutions for n=3: %e A224327 ..1..0..0....1..0..0....1..0..0....1..1..0....1..0..0....1..0..1....1..0..0 %e A224327 ..0..0..2....0..1..0....0..1..2....0..0..0....0..0..1....0..1..2....0..1..0 %e A224327 ..0..0..1....0..0..0....0..0..0....0..2..1....0..0..1....0..0..0....1..0..0 %Y A224327 Cf. A224333. %K A224327 nonn,easy %O A224327 1,2 %A A224327 _R. H. Hardin_, formula via _M. F. Hasler_ _William J. Keith_ and _Rob Pratt_ in the Sequence Fans Mailing List, Apr 03 2013