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 A169830 #36 Jun 12 2025 21:42:53
%S A169830 1,73,793,7993,79993,799993,7999993,79999993,799999993,7999999993,
%T A169830 79999999993,799999999993,7999999999993,79999999999993,
%U A169830 799999999999993,7999999999999993,79999999999999993,799999999999999993,7999999999999999993,79999999999999999993,799999999999999999993
%N A169830 Numbers k such that 2*reverse(k) - k = 1.
%C A169830 The sequence is infinite since it contains all numbers of the form 799...9993. (Cf. A101155, A101849.) [Ulrich Krug (leuchtfeuer37(AT)gmx.de), Jun 02 2010]
%C A169830 All numbers of the form 8*10^k-7 are members, but are there any others? - _Robert G. Wilson v_, Jun 01 2010
%C A169830 All solutions are of the form 8*10^k-7. - _David Radcliffe_, Jul 25 2015
%H A169830 Matthew House, <a href="/A169830/b169830.txt">Table of n, a(n) for n = 1..996</a>
%H A169830 Erich Friedman, <a href="https://erich-friedman.github.io/numbers.html">What's Special About This Number?</a> (See entry 73)
%H A169830 David Radcliffe, <a href="/A169830/a169830.pdf">Numbers that are nearly doubled when reversed</a>.
%H A169830 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-10).
%F A169830 a(n) = 8*10^(n-1) - 7. - _David Radcliffe_, Jul 25 2015
%F A169830 From _Matthew House_, Feb 12 2017: (Start)
%F A169830 G.f.: x*(1+62*x)/((1-x)*(1-10*x)).
%F A169830 a(n) = 11*a(n-1) - 10*a(n-2). (End)
%F A169830 E.g.f.: (31 - 35*exp(x) + 4*exp(10*x))/5. - _Elmo R. Oliveira_, Jun 12 2025
%t A169830 k = 1; lst = {}; fQ[n_] := 2 FromDigits@ Reverse@ IntegerDigits@n == 1 + n; While[k < 10^8, If[fQ@k, Print@k; AppendTo[lst, k]]; k++ ]; lst (* _Robert G. Wilson v_, Jun 01 2010 *)
%t A169830 Rest@ CoefficientList[Series[x (1 + 62 x)/((1 - x) (1 - 10 x)), {x, 0, 20}], x] (* or *)
%t A169830 Table[If[n == 1, 1, FromDigits@ Join[{7}, ConstantArray[9, n - 2], {3}]], {n, 20}] (* or *)
%t A169830 LinearRecurrence[{11, -10}, {1, 73}, 20] (* _Michael De Vlieger_, Feb 12 2017 *)
%o A169830 (PARI) isok(n) = 2*fromdigits(Vecrev(digits(n))) - n == 1; \\ _Michel Marcus_, Feb 12 2017
%Y A169830 Same sequence as A100412.
%Y A169830 Digit reversals of A083818.
%Y A169830 Cf. A101155, A101849.
%K A169830 nonn,base,easy
%O A169830 1,2
%A A169830 _N. J. A. Sloane_, May 31 2010
%E A169830 a(6)-a(8) from _Robert G. Wilson v_, Jun 01 2010
%E A169830 More terms from _David Radcliffe_, Jul 25 2015