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 A228840 #19 Mar 06 2020 13:45:27
%S A228840 2,15,171,2160,27783,358425,4626234,59716035,770832207,9950150160,
%T A228840 128439782811,1657942687845,21401266181778,276254540154855,
%U A228840 3565983915414819,46030886147041200,594181726489417887,7669891971371155905,99005472955353055626
%N A228840 a(n) = 3^n*A228569(n).
%C A228840 Bhadouria et al. call this the 3-binomial transform of the 3-Lucas sequence.
%H A228840 P. Bhadouria, D. Jhala, B. Singh, <a href="http://dx.doi.org/10.22436/jmcs.08.01.07">Binomial Transforms of the k-Lucas Sequences and its Properties</a>, The Journal of Mathematics and Computer Science (JMCS), Volume 8, Issue 1, Pages 81-92; sequence T_3.
%H A228840 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (15,-27).
%F A228840 G.f.: ( 2-15*x ) / ( 1-15*x+27*x^2 ).
%F A228840 Binomial transform of the binomial transform of A057076.
%t A228840 LinearRecurrence[{15,-27},{2,15},30] (* _Harvey P. Dale_, May 20 2018 *)
%K A228840 easy,nonn
%O A228840 0,1
%A A228840 _R. J. Mathar_, Nov 10 2013