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%I #13 Aug 04 2020 19:54:43
%S 35,46651605,62126595542551,82734857056306152425,
%T 110179167429819564875005515,146727139774551997160896788291901,
%U 195398586217617559179696685958485684415,260215032846061623065656040447357907946787025,346532002251364709713039450689133092337489050568051
%N Pentagonal numbers that are half other pentagonal numbers.
%H Colin Barker, <a href="/A107736/b107736.txt">Table of n, a(n) for n = 1..163</a>
%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1331715,-1331715,1).
%F a(n) = ((A001653(4n-2)^2-1)/24.
%F G.f.: -x*(x^2+41580*x+35) / ((x-1)*(x^2-1331714*x+1)). - _Colin Barker_, Jun 18 2015
%e a(2)=((A001653(6)^2-1)/24=(33461^2-1)/24=46651605.
%t LinearRecurrence[{1331715,-1331715,1},{35,46651605,62126595542551},20] (* _Harvey P. Dale_, Aug 04 2020 *)
%o (PARI) Vec(-x*(x^2+41580*x+35)/((x-1)*(x^2-1331714*x+1)) + O(x^20)) \\ _Colin Barker_, Jun 18 2015
%Y Cf. A001653, A000326.
%K nonn,easy
%O 1,1
%A _Franz Vrabec_, Aug 26 2006
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