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A166122
a(n) = (7-(-5)^n)/6.
2
1, 2, -3, 22, -103, 522, -2603, 13022, -65103, 325522, -1627603, 8138022, -40690103, 203450522, -1017252603, 5086263022, -25431315103, 127156575522, -635782877603, 3178914388022, -15894571940103, 79472859700522
OFFSET
0,2
FORMULA
a(n) = 5*a(n-2) - 4*a(n-1), a(0)= 1, a(1)= 2, for n>1.
a(n) = 7-5*a(n-1), a(0)=1.
a(n) = a(n-1)+(-5)^(n-1), a(0)=1.
O.g.f.: (1+6*x)/(1+4*x-5*x^2).
E.g.f.: (7*exp(x)-exp(-5*x))/6.
MATHEMATICA
LinearRecurrence[{-4, 5}, {1, 2}, 30] (* Harvey P. Dale, Mar 10 2016 *)
Table[(7 - (-5)^n)/6, {n, 24}] (* or *)
CoefficientList[Series[(1 + 6 x)/(1 + 4 x - 5 x^2), {x, 0, 24}], x] (* Michael De Vlieger, Apr 27 2016 *)
CROSSREFS
KEYWORD
sign,easy
AUTHOR
Philippe Deléham, Oct 07 2009
STATUS
approved