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a(n) = 12*n + 2.
18

%I #44 Sep 08 2022 08:44:43

%S 2,14,26,38,50,62,74,86,98,110,122,134,146,158,170,182,194,206,218,

%T 230,242,254,266,278,290,302,314,326,338,350,362,374,386,398,410,422,

%U 434,446,458,470,482,494,506,518,530,542,554,566,578,590,602,614,626,638

%N a(n) = 12*n + 2.

%C Apart from initial term(s), dimension of the space of weight 2n cusp forms for Gamma_0( 40 ).

%H Vincenzo Librandi, <a href="/A017545/b017545.txt">Table of n, a(n) for n = 0..2000</a>

%H Tanya Khovanova, <a href="http://www.tanyakhovanova.com/RecursiveSequences/RecursiveSequences.html">Recursive Sequences</a>.

%H William A. Stein, <a href="http://wstein.org/Tables/dimskg0n.gp">Dimensions of the spaces S_k(Gamma_0(N))</a>.

%H William A. Stein, <a href="http://wstein.org/Tables/">The modular forms database</a>.

%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1).

%F a(n) = 2*a(n-1) - a(n-2). - _Vincenzo Librandi_, Jun 07 2011

%F From _G. C. Greubel_, Sep 18 2019: (Start)

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

%F E.g.f.: 2*(1 + 6*x)*exp(x). (End)

%F Sum_{n>=0} (-1)^n/a(n) = Pi/12 + sqrt(3)*log(2 + sqrt(3))/12. - _Amiram Eldar_, Dec 12 2021

%p A017545:=n->12*n+2: seq(A017545(n), n=0..60); # _Wesley Ivan Hurt_, Apr 27 2017

%t 12*Range[0,60]+2 (* _Vladimir Joseph Stephan Orlovsky_, Feb 19 2011 *)

%o (Magma) [12*n+2: n in [0..60]]; // _Vincenzo Librandi_, Jun 07 2011

%o (PARI) a(n)=12*n+2 \\ _Charles R Greathouse IV_, Jul 10 2016

%o (Sage) [2*(6*n+1) for n in (0..60)] # _G. C. Greubel_, Sep 18 2019

%o (GAP) List([0..60], n-> 2*(6*n+1) ); # _G. C. Greubel_, Sep 18 2019

%Y Cf. A008594, A017533, A017557.

%Y Subsequence of A072065.

%K nonn,easy

%O 0,1

%A _N. J. A. Sloane_