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A254965 Indices of centered hexagonal numbers (A003215) that are also heptagonal numbers (A000566).

%I A254965 #6 Jun 13 2015 00:55:25
%S A254965 1,2,13,34,275,736,6027,16148,132309,354510,2904761,7783062,63772423,
%T A254965 170872844,1400088535,3751419496,30738175337,82360356058,674839768869,
%U A254965 1808176413770,14815736739771,39697520746872,325271368506083,871537280017404,7141154370394045
%N A254965 Indices of centered hexagonal numbers (A003215) that are also heptagonal numbers (A000566).
%C A254965 Also positive integers y in the solutions to 5*x^2 - 6*y^2 - 3*x + 6*y - 2 = 0, the corresponding values of x being A254964.
%H A254965 Colin Barker, <a href="/A254965/b254965.txt">Table of n, a(n) for n = 1..1000</a>
%H A254965 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,22,-22,-1,1).
%F A254965 a(n) = a(n-1)+22*a(n-2)-22*a(n-3)-a(n-4)+a(n-5).
%F A254965 G.f.: x*(x^3+11*x^2-x-1) / ((x-1)*(x^4-22*x^2+1)).
%e A254965 13 is in the sequence because the 13th centered hexagonal number is 469, which is also the 14th heptagonal number.
%o A254965 (PARI) Vec(x*(x^3+11*x^2-x-1)/((x-1)*(x^4-22*x^2+1)) + O(x^100))
%Y A254965 Cf. A000566, A003215, A254964, A254966.
%K A254965 nonn,easy
%O A254965 1,2
%A A254965 _Colin Barker_, Feb 11 2015