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A166544 a(n) = 7*n - a(n-1), with n>1, a(1)=2. 1
2, 12, 9, 19, 16, 26, 23, 33, 30, 40, 37, 47, 44, 54, 51, 61, 58, 68, 65, 75, 72, 82, 79, 89, 86, 96, 93, 103, 100, 110, 107, 117, 114, 124, 121, 131, 128, 138, 135, 145, 142, 152, 149, 159, 156, 166, 163, 173, 170, 180, 177, 187, 184, 194, 191, 201, 198, 208, 205 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
FORMULA
a(n) = (14*n + 13*(-1)^n + 7)/4. - Paolo P. Lava, Nov 10 2009
G.f.: -x*(-2-10*x+5*x^2)/((1+x)*(x-1)^2). - Vincenzo Librandi, Sep 13 2013
From G. C. Greubel, May 17 2016: (Start)
E.g.f.: (1/4)*(7*(1 + 2*x)*exp(x) + 13*exp(-x) - 20).
a(n) = a(n-1) + a(n-2) - a(n-3). (End)
Sum_{n>=1} (-1)^(n+1)/a(n) = 1/5 + tan(3*Pi/14)*Pi/7. - Amiram Eldar, Feb 23 2023
MATHEMATICA
CoefficientList[Series[-(- 2 - 10 x + 5 x^2)/((1 + x) (x - 1)^2), {x, 0, 80}], x] (* Vincenzo Librandi, Sep 13 2013 *)
LinearRecurrence[{1, 1, -1}, {2, 12, 9}, 50] (* G. C. Greubel, May 17 2016 *)
PROG
(Magma) [n eq 1 select 2 else 7*n-Self(n-1): n in [1..80]]; // Vincenzo Librandi, Sep 13 2013
CROSSREFS
Sequence in context: A229628 A002209 A100654 * A081468 A216349 A280015
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Oct 16 2009
STATUS
approved

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Last modified February 21 13:52 EST 2024. Contains 370235 sequences. (Running on oeis4.)