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A027658 a(n) = binomial(n+2, 2) + binomial(n+4, 5). 3

%I #22 Feb 27 2023 13:37:03

%S 1,4,12,31,71,147,280,498,837,1342,2068,3081,4459,6293,8688,11764,

%T 15657,20520,26524,33859,42735,53383,66056,81030,98605,119106,142884,

%U 170317,201811,237801,278752,325160,377553,436492,502572,576423,658711,750139,851448

%N a(n) = binomial(n+2, 2) + binomial(n+4, 5).

%H Vincenzo Librandi, <a href="/A027658/b027658.txt">Table of n, a(n) for n = 0..1000</a>

%H <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (6,-15,20,-15,6,-1).

%F G.f.: (1 - 2*x + 3*x^2 - x^3)/(1-x)^6. - _Colin Barker_, Apr 15 2013

%F From _R. J. Mathar_, Sep 29 2020: (Start)

%F a(n) = A000217(n+1) + A000389(n+4)

%F a(n) = (n+1)*(n+2)*(60 +12*n +7*n^2 +n^3)/120. (End)

%F From _G. C. Greubel_, Aug 01 2022: (Start)

%F a(n) = Sum_{j=1..2} binomial(n+2*j, 3*j-1).

%F E.g.f.: (1/120)*(120 + 360*x + 300*x^2 + 120*x^3 + 20*x^4 + x^5)*exp(x). (End)

%t CoefficientList[Series[(1-2*x+3*x^2-x^3)/(1-x)^6, {x, 0, 60}], x] (* _Vincenzo Librandi_, Oct 18 2013 *)

%t Sum[Binomial[2*j +Range[0, 60], 3*j-1], {j,2}] (* _G. C. Greubel_, Aug 01 2022 *)

%t LinearRecurrence[{6,-15,20,-15,6,-1},{1,4,12,31,71,147},40] (* _Harvey P. Dale_, Feb 27 2023 *)

%o (Magma) [(60 +12*n +7*n^2 +n^3)*Binomial(n+2,2)/60: n in [0..60]]; // _G. C. Greubel_, Aug 01 2022

%o (SageMath) [(60 +12*n +7*n^2 +n^3)*binomial(n+2,2)/60 for n in (0..60)] # _G. C. Greubel_, Aug 01 2022

%Y Cf. A000217, A000389.

%K nonn,easy

%O 0,2

%A _N. J. A. Sloane_

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Last modified March 29 06:34 EDT 2024. Contains 371265 sequences. (Running on oeis4.)