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A168401
a(n) = 4 + 9*floor(n/2).
1
4, 13, 13, 22, 22, 31, 31, 40, 40, 49, 49, 58, 58, 67, 67, 76, 76, 85, 85, 94, 94, 103, 103, 112, 112, 121, 121, 130, 130, 139, 139, 148, 148, 157, 157, 166, 166, 175, 175, 184, 184, 193, 193, 202, 202, 211, 211, 220, 220, 229, 229, 238, 238, 247, 247, 256, 256
OFFSET
1,1
FORMULA
a(n) = 9*n - a(n-1) - 1, with n > 1, a(1)=4.
G.f.: x*(4 + 9*x - 4*x^2)/((1+x)*(x-1)^2). - Vincenzo Librandi, Sep 18 2013
a(n) = a(n-1) + a(n-2) - a(n-3). - Vincenzo Librandi, Sep 18 2013
E.g.f.: (1/4)*(9 - 16*exp(x) + (7 + 18*x)*exp(2*x))*exp(-x). - G. C. Greubel, Jul 21 2016
MATHEMATICA
Table[4 + 9 Floor[n/2], {n, 60}] (* Vincenzo Librandi, Sep 18 2013 *)
PROG
(Magma) [4+9*Floor(n/2): n in [1..60]]; // Bruno Berselli, Sep 18 2013
(PARI) a(n)=n\2*9 + 4 \\ Charles R Greathouse IV, Jul 21 2016
CROSSREFS
Cf. A017209.
Sequence in context: A050223 A301792 A344512 * A370644 A081738 A232496
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Nov 25 2009
EXTENSIONS
New definition by Vincenzo Librandi Sep 18 2013
STATUS
approved