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 A269457 a(n) = 5*(n + 1)*(n + 4)/2. 1

%I

%S 10,25,45,70,100,135,175,220,270,325,385,450,520,595,675,760,850,945,

%T 1045,1150,1260,1375,1495,1620,1750,1885,2025,2170,2320,2475,2635,

%U 2800,2970,3145,3325,3510,3700,3895,4095,4300,4510,4725,4945,5170,5400,5635

%N a(n) = 5*(n + 1)*(n + 4)/2.

%C More generally, the ordinary generating function for the sequences of the form k*(n + 1)*(n - 1 + k)/2 is (k*(k - 1)/2 + (k*(3 - k)/2)*x)/(1 - x)^3(see links section).

%H Ilya Gutkovskiy, <a href="/A269457/a269457.pdf">Sequences of the form k*(n + 1)*(n - 1 + k)/2</a>

%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1).

%F G.f.: 5*(2 - x)/(1 -x)^3.

%F a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3).

%F a(n) = Sum_{k=0..n} 5*(k + 2) = Sum_{k=0..n} A008587(k + 2).

%F Sum_{n>=0} 1/a(n) = 11/45 = 0.24444444444... = A040002.

%F a(n) = 5*A000096(n+1).

%F a(n) = A055998(2*n+2) + A055998(n+1). - _Bruno Berselli_, Sep 23 2016

%e a(0) = 0 + 1 + 2 + 3 + 4 = 10;

%e a(1) = 0 + 1 + 2 + 3 + 4 + 1 + 2 + 3 + 4 + 5 = 25;

%e a(2) = 0 + 1 + 2 + 3 + 4 + 1 + 2 + 3 + 4 + 5 + 2 + 3 + 4 + 5 + 6 = 45, etc.

%t Table[5 (n + 1) ((n + 4)/2), {n, 0, 45}]

%t Table[Sum[5 (k + 2), {k, 0, n}], {n, 0, 45}]

%t LinearRecurrence[{3, -3, 1}, {10, 25, 45}, 46]

%o (MAGMA) [5*(n+1)*(n+4)/2: n in [0..50]]; // _Vincenzo Librandi_, Feb 28 2016

%o (PARI) a(n) = 5*(n + 1)*(n + 4)/2; \\ _Michel Marcus_, Feb 29 2016

%o (PARI) Vec(5*(2-x)/(1-x)^3 + O(x^100)) \\ _Altug Alkan_, Mar 04 2016

%Y Cf. A000096, A008587, A028895, A040002, A045943, A055998, A054000, A067728.

%K nonn,easy

%O 0,1

%A _Ilya Gutkovskiy_, Feb 27 2016

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Last modified January 17 22:48 EST 2019. Contains 319251 sequences. (Running on oeis4.)