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 A083818 #23 Jun 12 2025 21:43:29
%S A083818 1,37,397,3997,39997,399997,3999997,39999997,399999997,3999999997,
%T A083818 39999999997,399999999997,3999999999997,39999999999997,
%U A083818 399999999999997,3999999999999997,39999999999999997,399999999999999997,3999999999999999997,39999999999999999997,399999999999999999997
%N A083818 Numbers k such that 2k-1 is the digit reversal of k.
%C A083818 a(n) = 1 + 36 + 360 + 3600 + 36000 + ..., for a total of n terms. a(n) = 1 + sum of first n-1 terms of the geometric progression with first term 36 and common ratio 10. a(n) = 1 + 36*A000042(n-1) (the unary sequence).
%H A083818 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-10).
%F A083818 a(n) = 4*10^(n-1) - 3.
%F A083818 From _Elmo R. Oliveira_, Jun 12 2025: (Start)
%F A083818 G.f.: x*(26*x+1)/((x-1)*(10*x-1)).
%F A083818 E.g.f.: (13 - 15*exp(x) + 2*exp(10*x))/5.
%F A083818 a(n) = 11*a(n-1) - 10*a(n-2) for n >= 3. (End)
%e A083818 2*37 - 1 = 73.
%o A083818 (PARI) my(x='x+O('x^22)); Vec(x*(1+26*x)/((1-x)*(1-10*x))) \\ _Elmo R. Oliveira_, Jun 12 2025
%Y A083818 Cf. A000042, A083811, A083812, A083813.
%Y A083818 Digit reversals of A169830.
%K A083818 base,easy,nonn
%O A083818 1,2
%A A083818 _Amarnath Murthy_ and Meenakshi Srikanth (menakan_s(AT)yahoo.com), May 08 2003
%E A083818 a(1)=1 inserted by _David Radcliffe_, Jul 25 2015