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 A258340 #54 Sep 08 2022 08:46:12
%S A258340 1,7,46,310,2131,14797,103216,721420,5046661,35316787,247187986,
%T A258340 1730227330,12111325591,84778481977,593446982356,4154121702040,
%U A258340 29078830390921,203551748166367,1424862043454326,9974033723049550,69818234317954651,488727634995505957
%N A258340 a(n) = (7^n + 3^n - 2)/8.
%C A258340 This sequence appeared on an test given to job interviewers.
%H A258340 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (11,-31,21).
%F A258340 a(n) = (A074608(n) - 2)/8. - _Michel Marcus_, Aug 20 2015
%F A258340 G.f.: x*(1-4*x)/((1-x)*(1-3*x)*(1-7*x)). - _Vincenzo Librandi_, Aug 22 2015
%F A258340 a(n) = 11*a(n-1) - 31*a(n-2) + 21*a(n-3) with n>2, a(0)=0. - _Bruno Berselli_, Aug 24 2015
%F A258340 a(n) = Sum_{k=1..n} A027907(n,2k)*4^(k-1) . - _J. Conrad_, Aug 30 2016
%t A258340 Table[(7^n + 3^n - 2)/8, {n, 1, 30}] (* _Bruno Berselli_, Aug 24 2015 *)
%t A258340 LinearRecurrence[{11,-31,21},{1,7,46},30] (* _Harvey P. Dale_, May 01 2018 *)
%o A258340 (PARI) first(m)=vector(m,i,(3^i+7^i-2)/8) \\ _Anders Hellström_, Aug 20 2015
%o A258340 (Magma) [(3^n+7^n-2)/8: n in [1..30]]; // _Vincenzo Librandi_, Aug 22 2015
%o A258340 (Sage) [(7^n+3^n-2)/8 for n in (1..30)] # _Bruno Berselli_, Aug 24 2015
%Y A258340 Cf. A074608.
%K A258340 nonn,easy
%O A258340 1,2
%A A258340 _Edwin McCravy_, Aug 05 2015