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 A180847 #24 Sep 01 2025 11:22:10
%S A180847 0,1,31,853,23095,623821,16844191,454797253,12279542215,331547705341,
%T A180847 8951788306351,241698285320053,6525853707835735,176198050128342061,
%U A180847 4757347353532344511,128448378545641737253,3468106220733400647655
%N A180847 a(n) = (27^n-4^n)/23.
%C A180847 For n>0, a(n) appears in several triangle sums of Nicomachus' table A036561, i.e. Ze1(2*n), Ze1(2*n+1)/2; Ze4(3*n), Ze4(3*n+1)/3 and Ze4(3*n+2)/9. See A180662 for information about these zebra and other chess sums.
%H A180847 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (31,-108).
%F A180847 a(n) = (27^n-4^n)/23.
%F A180847 G.f.: x/((27*x-1)*(4*x-1)).
%F A180847 a(0)=0, a(1)=1, a(n) = 31*a(n-1)-108*a(n-2). - _Harvey P. Dale_, Sep 01 2011
%t A180847 Table[(27^n-4^n)/23,{n,0,20}] (* or *) LinearRecurrence[{31,-108},{0,1},20] (* _Harvey P. Dale_, Sep 01 2011 *)
%o A180847 (PARI) a(n)=(27^n-4^n)/23 \\ _Charles R Greathouse IV_, Oct 07 2015
%Y A180847 Cf. A016153, A016140, A180844, A180845, A180846, A180847, A016185.
%K A180847 easy,nonn,changed
%O A180847 0,3
%A A180847 _Johannes W. Meijer_, Sep 21 2010