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 A224328 #12 Jun 02 2025 08:30:52 %S A224328 1,14,93,508,2555,12282,57337,262136,1179639,5242870,23068661, %T A224328 100663284,436207603,1879048178,8053063665,34359738352,146028888047, %U A224328 618475290606,2611340115949,10995116277740,46179488366571,193514046488554 %N A224328 Number of idempotent n X n 0..3 matrices of rank n-1. %C A224328 Column 3 of A224333 %H A224328 R. H. Hardin, <a href="/A224328/b224328.txt">Table of n, a(n) for n = 1..210</a> %H A224328 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (10,-33,40,-16). %F A224328 a(n) = n*(2*4^(n-1)-1). %F A224328 a(n) = 10*a(n-1) -33*a(n-2) +40*a(n-3) -16*a(n-4). %F A224328 G.f.: -x*(-1-4*x+14*x^2) / ( (4*x-1)^2*(x-1)^2 ). - _R. J. Mathar_, Oct 21 2014 %e A224328 Some solutions for n=3 %e A224328 ..0..1..3....1..0..0....0..0..0....0..0..0....0..1..0....1..3..0....1..0..0 %e A224328 ..0..1..0....0..0..1....0..1..0....2..1..0....0..1..0....0..0..0....0..1..0 %e A224328 ..0..0..1....0..0..1....1..0..1....0..0..1....0..0..1....0..3..1....0..3..0 %K A224328 nonn,easy %O A224328 1,2 %A A224328 _R. H. Hardin_, formula via _M. F. Hasler_ _William J. Keith_ and Rob Pratt in the Sequence Fans Mailing List, Apr 03 2013