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A155628
a(n) = 7^n-4^n+1^n.
21
1, 4, 34, 280, 2146, 15784, 113554, 807160, 5699266, 40091464, 281426674, 1973132440, 13824509986, 96821901544, 677954637394, 4746487768120, 33228635602306, 232613334118024, 1628344878433714, 11398620307466200
OFFSET
0,2
FORMULA
G.f.: 1/(1-7*x)-1/(1-4*x)+1/(1-x). E.g.f.: e^(7*x)-e^(4*x)+e^x.
a(n) = 11*a(n-1)-28*a(n-2)+18 with a(0)=1, a(1)=4. - Vincenzo Librandi, Jul 21 2010
MATHEMATICA
Table[7^n-4^n+1, {n, 0, 20}] (* or *) LinearRecurrence[{12, -39, 28}, {1, 4, 34}, 20] (* Harvey P. Dale, Jul 16 2017 *)
PROG
(PARI) a(n)=7^n-4^n+1 \\ Charles R Greathouse IV, Sep 24 2015
KEYWORD
nonn,easy
AUTHOR
Mohammad K. Azarian, Jan 30 2009
STATUS
approved