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A081661
Partial sums of A081660.
1
1, 3, 8, 16, 31, 57, 106, 198, 377, 727, 1420, 2796, 5539, 11013, 21950, 43810, 87517, 174915, 349696, 699240, 1398311, 2796433, 5592658, 11185086, 22369921, 44739567, 89478836, 178957348, 357914347, 715828317, 1431656230, 2863312026
OFFSET
0,2
FORMULA
a(n) = 2^(n+2)/3+(n^2+n-1)/2+(-1)^n/6.
G.f.: (1-x-2*x^3)/((1+x)*(1-2*x)*(1-x)^3). - Bruno Berselli, Aug 11 2013
MAPLE
A081661:=n->2^(n+2)/3 + (n^2+n-1)/2 + (-1)^n/6; seq(A081661(n), n=0..30); # Wesley Ivan Hurt, May 07 2014
MATHEMATICA
Table[2^(n + 2) / 3 + (n^2 + n - 1) / 2 + (-1)^n / 6, {n, 0, 40}] (* Vincenzo Librandi, Aug 10 2013 *)
LinearRecurrence[{4, -4, -2, 5, -2}, {1, 3, 8, 16, 31}, 40] (* Harvey P. Dale, Jan 11 2016 *)
PROG
(Magma) [2^(n+2)/3+(n^2+n-1)/2+(-1)^n/6: n in [0..40]]; // Vincenzo Librandi, Aug 10 2013
CROSSREFS
Sequence in context: A295960 A068039 A188123 * A005103 A001978 A173283
KEYWORD
nonn,easy
AUTHOR
Paul Barry, Mar 26 2003
STATUS
approved