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 A355492 #41 Jun 10 2024 06:14:10 %S A355492 5,19,61,187,565,1699,5101,15307,45925,137779,413341,1240027,3720085, %T A355492 11160259,33480781,100442347,301327045,903981139,2711943421, %U A355492 8135830267,24407490805,73222472419,219667417261,659002251787,1977006755365,5931020266099,17793060798301,53379182394907 %N A355492 a(n) = 7*3^n - 2. %C A355492 Right ending points of the gaps in A171884. The left ending points are given in A198643. %H A355492 Jianing Song, <a href="/A355492/b355492.txt">Table of n, a(n) for n = 0..1000</a> %H A355492 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (4,-3). %F A355492 G.f.: (5-x)/((1-x)*(1-3*x)). %F A355492 E.g.f.: 7*exp(3*x) - 2*exp(x). %e A355492 The numbers not appearing in A171884 are those in the range [5*3^k-1, 7*3^k-2] for some k; that is, [4, 5] U [14, 19] U [44, 61] U ... %t A355492 7*3^Range[0, 50] - 2 (* _Paolo Xausa_, Jun 10 2024 *) %o A355492 (PARI) a(n)=7*3^n-2 %Y A355492 Cf. A171884, A198643. %K A355492 nonn,easy %O A355492 0,1 %A A355492 _Jianing Song_, Oct 07 2022