OFFSET
0,3
COMMENTS
Sum_{i = 1 .. n} (i^2 + i - 2)/2^i = a(n)/2^n so we see that the sum approaches 6 as n gets large.
FORMULA
O.g.f.: (4 - 2x)*x^2/((1 - x)^3*(1 - 2x)).
MATHEMATICA
RecurrenceTable[{a[n] == 2a[n - 1] + n^2 + n - 2, a[1] == 0}, a, {n, 1, 25}]
Table[6*2^n - n^2 - 5*n - 6, {n, 0, 30}] (* T. D. Noe, Oct 01 2013 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Geoffrey Critzer, Sep 29 2013
STATUS
approved