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 A332186 #14 Jul 13 2024 20:25:15
%S A332186 6,868,88688,8886888,888868888,88888688888,8888886888888,
%T A332186 888888868888888,88888888688888888,8888888886888888888,
%U A332186 888888888868888888888,88888888888688888888888,8888888888886888888888888,888888888888868888888888888,88888888888888688888888888888,8888888888888886888888888888888
%N A332186 a(n) = 8*(10^(2n+1)-1)/9 - 2*10^n.
%H A332186 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (111,-1110,1000).
%F A332186 a(n) = 8*A138148(n) + 6*10^n = A002282(2n+1) - 2*10^n = 2*A332143(n).
%F A332186 G.f.: (6 + 202*x - 1000*x^2)/((1 - x)(1 - 10*x)(1 - 100*x)).
%F A332186 a(n) = 111*a(n-1) - 1110*a(n-2) + 1000*a(n-3) for n > 2.
%F A332186 E.g.f.: 2*exp(x)*(40*exp(99*x) - 9*exp(9*x) - 4)/9. - _Stefano Spezia_, Jul 13 2024
%p A332186 A332186 := n -> 8*(10^(2*n+1)-1)/9-2*10^n;
%t A332186 Array[8 (10^(2 # + 1)-1)/9 - 2*10^# &, 15, 0]
%t A332186 LinearRecurrence[{111,-1110,1000},{6,868,88688},20] (*or *) Table[FromDigits[Join[PadRight[ {},n,8],PadRight[ {6},n+1,8]]],{n,0,20}] (* _Harvey P. Dale_, May 30 2023 *)
%o A332186 (PARI) apply( {A332186(n)=10^(n*2+1)\9*8-2*10^n}, [0..15])
%o A332186 (Python) def A332186(n): return 10**(n*2+1)//9*8-2*10**n
%Y A332186 Cf. A002275 (repunits R_n = (10^n-1)/9), A002282 (8*R_n), A011557 (10^n).
%Y A332186 Cf. A138148 (cyclops numbers with binary digits), A002113 (palindromes).
%Y A332186 Cf. A332180 .. A332189 (variants with different middle digit 0, ..., 9).
%K A332186 nonn,base,easy
%O A332186 0,1
%A A332186 _M. F. Hasler_, Feb 08 2020