OFFSET
1,2
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (5,-9,7,-2).
FORMULA
a(n) = 2^n-(n-1)*(n-2)/2-n+1 for n>1. - Lambert Herrgesell (zero815(AT)googlemail.com), Mar 14 2006
a(n) = A014844(n), n>1. - R. J. Mathar, Sep 19 2008
From Colin Barker, Dec 18 2012: (Start)
a(n) = 5*a(n-1)-9*a(n-2)+7*a(n-3)-2*a(n-4) for n>5.
G.f.: -x*(2*x^4-5*x^3+x^2+2*x-1) / ((x-1)^3*(2*x-1)). (End)
MATHEMATICA
Join[{1}, Array[2^# - #*(# - 1)/2 &, 50, 2]] (* Paolo Xausa, Mar 16 2024 *)
PROG
(Magma) [1] cat[2^n-(n-1)*(n-2)/2-n+1: n in [2..40]]; // Vincenzo Librandi, Apr 18 2012
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Amarnath Murthy, Mar 21 2003
EXTENSIONS
More terms from Lambert Herrgesell (zero815(AT)googlemail.com), Mar 14 2006
STATUS
approved