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 A002281 #53 Jul 21 2025 00:25:50
%S A002281 0,7,77,777,7777,77777,777777,7777777,77777777,777777777,7777777777,
%T A002281 77777777777,777777777777,7777777777777,77777777777777,
%U A002281 777777777777777,7777777777777777,77777777777777777,777777777777777777,7777777777777777777,77777777777777777777,777777777777777777777
%N A002281 a(n) = 7*(10^n - 1)/9.
%H A002281 Ivan Panchenko, <a href="/A002281/b002281.txt">Table of n, a(n) for n = 0..200</a>
%H A002281 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-10).
%F A002281 a(n) = A178634(n)/A002283(n). - _Reinhard Zumkeller_, May 31 2010
%F A002281 From _Vincenzo Librandi_, Jul 22 2010: (Start)
%F A002281 a(n) = a(n-1) + 7*10^(n-1) with n>0, a(0)=0.
%F A002281 a(n) = 11*a(n-1) - 10*a(n-2) with n>1, a(0)=0, a(1)=7. (End)
%F A002281 G.f.: 7*x/((x-1)*(10*x-1)). - _Colin Barker_, Jan 24 2013
%F A002281 a(n) = 7*A002275(n). - _Wesley Ivan Hurt_, Mar 24 2015
%F A002281 E.g.f.: 7*exp(x)*(exp(9*x) - 1)/9. - _Stefano Spezia_, Sep 13 2023
%F A002281 From _Elmo R. Oliveira_, Jul 20 2025: (Start)
%F A002281 a(n) = (A099915(n) - 1)/2.
%F A002281 a(n) = A010785(A017245(n-1)) for n >= 1. (End)
%p A002281 A002281:=n->7*(10^n-1)/9: seq(A002281(n), n=0..30); # _Wesley Ivan Hurt_, Mar 24 2015
%t A002281 LinearRecurrence[{11,-10},{0,7},25] (* _Robert G. Wilson v_, Jul 06 2013 *)
%o A002281 (Magma) [7*(10^n-1)/9 : n in [0..30]]; // _Wesley Ivan Hurt_, Mar 24 2015
%o A002281 (PARI) a(n)=7*(10^n-1)/9 \\ _Charles R Greathouse IV_, Sep 24 2015
%Y A002281 Cf. A002275, A002276, A002277, A002278, A002279, A002280, A002282, A002283, A178630, A178634.
%Y A002281 Cf. A010785, A017245, A099915.
%K A002281 easy,nonn
%O A002281 0,2
%A A002281 _N. J. A. Sloane_