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 A247842 #20 Jan 14 2025 11:05:43
%S A247842 0,81,810,7371,66420,597861,5380830,48427551,435848040,3922632441,
%T A247842 35303692050,317733228531,2859599056860,25736391511821,
%U A247842 231627523606470,2084647712458311,18761829412124880,168856464709124001,1519708182382116090,13677373641439044891
%N A247842 a(n) = Sum_{k=2..n} 9^k.
%H A247842 Vincenzo Librandi, <a href="/A247842/b247842.txt">Table of n, a(n) for n = 1..200</a>
%H A247842 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (10,-9).
%F A247842 G.f.: 81*x^2/((1-x)*(1-9*x)).
%F A247842 a(n) = a(n-1) + 9^n = (9^(n+1) - 81)/8 = 10*a(n-1) - 9*a(n-2).
%F A247842 a(n) = A052386(n) - 9. - _Michel Marcus_, Sep 25 2014
%p A247842 A247842:=n->add(9^k, k=2..n): seq(A247842(n), n=1..30); # _Wesley Ivan Hurt_, Sep 26 2014
%t A247842 RecurrenceTable[{a[1] == 0, a[n] == a[n-1] + 9^n}, a, {n, 30}] (* or *) CoefficientList[Series[81 x / ((1 - x) (1 - 9 x)), {x, 0, 30}], x]
%o A247842 (Magma) [0] cat [&+[9^k: k in [2..n]]: n in [2..30]];
%o A247842 (Magma) [(9^(n+1)-81)/8: n in [1..30]];
%Y A247842 Cf. similar sequences listed in A247817.
%Y A247842 Cf. A052386.
%K A247842 nonn,easy
%O A247842 1,2
%A A247842 _Vincenzo Librandi_, Sep 25 2014