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 A086574 #32 Sep 12 2024 17:08:08
%S A086574 0,27,297,2997,29997,299997,2999997,29999997,299999997,2999999997,
%T A086574 29999999997,299999999997,2999999999997,29999999999997,
%U A086574 299999999999997,2999999999999997,29999999999999997,299999999999999997,2999999999999999997,29999999999999999997,299999999999999999997
%N A086574 a(n) = 3*(10^n - 1).
%C A086574 Original definition: a(n) = k where R(k+3) = 3. [Here R = reverse = A004086, not R = repunit = A002275 as in some other places.]
%C A086574 The restriction to positive indices yields A083813. - _M. F. Hasler_, Jul 29 2016
%H A086574 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-10).
%F A086574 a(n) = 3*9*A002275(n) = 3*A002283(n).
%F A086574 R(a(n)) = A086579(n).
%F A086574 a(n) = 11*a(n-1) - 10*a(n-2) with a(0)=0 and a(1)=27. - _Harvey P. Dale_, Nov 28 2015
%F A086574 G.f.: 27*x/((1 - x)*(1 - 10*x)). - _Ilya Gutkovskiy_, Jul 29 2016
%F A086574 E.g.f.: 3*exp(x)*(exp(9*x) - 1). - _Elmo R. Oliveira_, Sep 12 2024
%t A086574 Join[{0},Table[FromDigits[Join[PadRight[{2},n,9],{7}]],{n,20}]] (* or *) LinearRecurrence[{11,-10},{0,27},30] (* _Harvey P. Dale_, Nov 28 2015 *)
%o A086574 (PARI) a(n)=10^n*3-3 \\ _M. F. Hasler_, Jul 29 2016
%Y A086574 Cf. A002275, A004086 (R(n)), A083813.
%Y A086574 Cf. One of family of sequences of form a(n) = k, where R(k+m) = m, m=1 to 9; m=1: A002283, m=2: A086573, m=3: A086574, m=4: A086575, m=5: A086576, m=6: A086577, m=7: A086578, m=8: A086579, m=9: A086580.
%K A086574 nonn,easy
%O A086574 0,2
%A A086574 _Ray Chandler_, Jul 22 2003
%E A086574 Edited by _M. F. Hasler_, Jul 29 2016