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 A342405 #12 Mar 11 2021 11:44:58 %S A342405 0,45,2268,76221,2245320,62858025,1723364748,46836754821, %T A342405 1268169391440,34282547074305,926123262507828,25011175461289821, %U A342405 675371104361586360,18235844869321055385,492377645105637260508,13294313813660319607221,358947876218708733778080 %N A342405 a(n) = (27^n - 3*9^n - 3*12^n)/6 + 6^n. %H A342405 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (54,-963,6966,-17496). %F A342405 From _Chai Wah Wu_, Mar 11 2021: (Start) %F A342405 a(n) = 54*a(n-1) - 963*a(n-2) + 6966*a(n-3) - 17496*a(n-4) for n > 4. %F A342405 G.f.: 9*x^2*(-324*x^2 - 18*x + 5)/((6*x - 1)*(9*x - 1)*(12*x - 1)*(27*x - 1)). (End) %F A342405 a(n) == 0 (mod 81) for n >= 3. - _Hugo Pfoertner_, Mar 11 2021 %Y A342405 Column 3 of A342202. %K A342405 nonn %O A342405 1,2 %A A342405 _Petros Hadjicostas_, Mar 10 2021