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 A196661 #24 Mar 18 2025 15:11:18
%S A196661 1,5,35,245,1715,12005,84035,588245,4117715,28824005,201768035,
%T A196661 1412376245,9886633715,69206436005,484445052035,3391115364245,
%U A196661 23737807549715,166164652848005,1163152569936035,8142067989552245,56994475926865715,398961331488060005
%N A196661 Expansion of g.f. (1-2*x)/(1-7*x).
%H A196661 <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (7).
%F A196661 a(0) = 1, a(n) = 5*7^(n-1) for n>0.
%F A196661 a(n) = Sum_{k=0..n} A193722(n,k)*2^k.
%F A196661 From _Elmo R. Oliveira_, Mar 18 2025: (Start)
%F A196661 E.g.f.: (5*exp(7*x) + 2)/7.
%F A196661 a(n) = 7*a(n-1). (End)
%o A196661 (PARI) a(n)=if(n,5*7^(n-1),1) \\ _Charles R Greathouse IV_, Nov 21 2011
%Y A196661 Cf. A002001, A193577 (which is the same except for the initial 1), A193722.
%K A196661 nonn,easy
%O A196661 0,2
%A A196661 _Philippe Deléham_, Oct 05 2011