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A047280
Numbers that are congruent to {3, 6} mod 7.
7
3, 6, 10, 13, 17, 20, 24, 27, 31, 34, 38, 41, 45, 48, 52, 55, 59, 62, 66, 69, 73, 76, 80, 83, 87, 90, 94, 97, 101, 104, 108, 111, 115, 118, 122, 125, 129, 132, 136, 139, 143, 146, 150, 153, 157, 160, 164, 167, 171, 174, 178, 181, 185, 188, 192, 195, 199, 202
OFFSET
1,1
FORMULA
a(n) = 7*n - a(n-1) - 5 with n > 1, a(1)=3. - Vincenzo Librandi, Aug 05 2010
G.f.: x*(3 + 3*x + x^2) / ( (1+x)*(x-1)^2 ). - R. J. Mathar, Oct 25 2011
a(n) = 3*n + ceiling(n/2) - 1. - Arkadiusz Wesolowski, Sep 20 2012
a(n) = 4n - 1 - floor(n/2). - Wesley Ivan Hurt, Oct 16 2013
E.g.f.: 1 + ((14*x - 3)*exp(x) - exp(-x))/4. - David Lovler, Sep 14 2022
MAPLE
A047280:=n->4*n-1-floor(n/2); seq(A047280(k), k=1..100); # Wesley Ivan Hurt, Oct 16 2013
MATHEMATICA
Flatten[#+{3, 6}&/@(7Range[0, 30])] (* Harvey P. Dale, Jan 11 2011 *)
PROG
(PARI) a(n) = 4*n - 1 - floor(n/2) \\ David Lovler, Sep 14 2022
CROSSREFS
Sequence in context: A258834 A329997 A194028 * A310054 A310055 A356086
KEYWORD
nonn,easy
STATUS
approved