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 A173772 #22 Sep 09 2024 20:38:25
%S A173772 7,47,447,4447,44447,444447,4444447,44444447,444444447,4444444447,
%T A173772 44444444447,444444444447,4444444444447,44444444444447,
%U A173772 444444444444447,4444444444444447,44444444444444447,444444444444444447,4444444444444444447,44444444444444444447,444444444444444444447
%N A173772 a(n) = (4*10^n + 23)/9.
%H A173772 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-10).
%F A173772 a(n) = 10*a(n-1) - 23 with n > 1, a(1) = 7.
%F A173772 a(n) = 11*a(n-1) - 10*a(n-2). G.f.: -x*(30*x-7)/((x-1)*(10*x-1)). [_Colin Barker_, Jan 24 2013]
%F A173772 E.g.f.: exp(x)*(4*exp(9*x) + 23)/9. - _Elmo R. Oliveira_, Sep 09 2024
%t A173772 LinearRecurrence[{11,-10},{7,47},30] (* or *) Table[FromDigits[ PadLeft[ {7},n,4]],{n,30}] (* _Harvey P. Dale_, Dec 27 2014 *)
%o A173772 (PARI) a(n)=4*10^n\9+3 \\ _Charles R Greathouse IV_, Jan 11 2012
%Y A173772 Cf. A173771 (primes).
%K A173772 nonn,easy
%O A173772 1,1
%A A173772 _Vincenzo Librandi_, Feb 24 2010
%E A173772 a(19)-a(21) from _Elmo R. Oliveira_, Sep 09 2024