A355492 - OEIS

%I #41 Jun 10 2024 06:14:10

%S 5,19,61,187,565,1699,5101,15307,45925,137779,413341,1240027,3720085,

%T 11160259,33480781,100442347,301327045,903981139,2711943421,

%U 8135830267,24407490805,73222472419,219667417261,659002251787,1977006755365,5931020266099,17793060798301,53379182394907

%N a(n) = 7*3^n - 2.

%C Right ending points of the gaps in A171884. The left ending points are given in A198643.

%H Jianing Song, <a href="/A355492/b355492.txt">Table of n, a(n) for n = 0..1000</a>

%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (4,-3).

%F G.f.: (5-x)/((1-x)*(1-3*x)).

%F E.g.f.: 7*exp(3*x) - 2*exp(x).

%e 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 7*3^Range[0, 50] - 2 (* _Paolo Xausa_, Jun 10 2024 *)

%o (PARI) a(n)=7*3^n-2

%Y Cf. A171884, A198643.

%K nonn,easy

%O 0,1

%A _Jianing Song_, Oct 07 2022