A118058 a(n) = 49n^2 - 28n - 20.
1, 120, 337, 652, 1065, 1576, 2185, 2892, 3697, 4600, 5601, 6700, 7897, 9192, 10585, 12076, 13665, 15352, 17137, 19020, 21001, 23080, 25257, 27532, 29905, 32376, 34945, 37612, 40377, 43240, 46201, 49260, 52417, 55672, 59025, 62476, 66025
Offset: 1
Examples
a(3)=49*3^2-28*3-20=337, a(4)=49*4^2-28*4-20=652 and 337+338+...+518=519+...+651.
Links
- Vincenzo Librandi, Table of n, a(n) for n = 1..1000
- Index entries for linear recurrences with constant coefficients, signature (3,-3,1).
Programs
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Magma
[49*n^2-28*n-20: n in [1..50]]; // Vincenzo Librandi, Jul 08 2012
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Mathematica
Table[49*n^2 - 28*n - 20, {n, 10}] (* Vincenzo Librandi, Jul 08 2012 *)
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PARI
a(n)=49*n^2-28*n-20 \\ Charles R Greathouse IV, Jun 17 2017
Formula
a(n)+(a(n)+1)+...+(a(n)+98n+34)=7(7n-2)(7n+5)(14n+3)/2; e.g., 337+338+...+518=77805=7*19*26*45/2.
a(n) = 3*a(n-1)-3*a(n-2)+a(n-3). G.f.: x*(1+117*x-20*x^2)/(1-x)^3. - Colin Barker, Jun 30 2012
Extensions
Corrected by Franklin T. Adams-Watters and T. D. Noe, Oct 25 2006
Comments