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 A221909 #31 Apr 12 2025 18:23:57
%S A221909 1,14,63,364,2429,16842,117691,823592,5764857,40353670,282475319,
%T A221909 1977326820,13841287285,96889010498,678223072947,4747561510048,
%U A221909 33232930569713,232630513987326,1628413597910575,11398895185373276,79792266297612141,558545864083284154,3909821048582988203
%N A221909 a(n) = 7^n + 7*n.
%H A221909 Vincenzo Librandi, <a href="/A221909/b221909.txt">Table of n, a(n) for n = 0..500</a>
%H A221909 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (9,-15,7).
%F A221909 G.f.: (1+5*x-48*x^2)/((1-x)^2*(1-7*x)).
%F A221909 a(n) = 9*a(n-1) - 15*a(n-2) + 7*a(n-3).
%F A221909 a(n) = A176972(n) - 1.
%F A221909 E.g.f.: exp(x)*(exp(6*x) + 7*x). - _Elmo R. Oliveira_, Sep 10 2024
%t A221909 Table[(7^n + 7 n), {n, 0, 30}] (* or *) CoefficientList[Series[(1 + 5 x - 48 x^2)/((1 - x)^2 (1 - 7 x)), {x, 0, 30}], x]
%o A221909 (Magma) [7^n + 7*n: n in [0..30]];
%o A221909 (Magma) I:=[1, 14, 63]; [n le 3 select I[n] else 9*Self(n-1)-15*Self(n-2)+7*Self(n-3): n in [1..30]];
%o A221909 (PARI) a(n)=7^n+7*n \\ _Charles R Greathouse IV_, Apr 18 2013
%Y A221909 Cf. A176972, A198397.
%K A221909 nonn,easy
%O A221909 0,2
%A A221909 _Vincenzo Librandi_, Mar 02 2013