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%I #8 Sep 08 2022 08:44:40
%S 1,4,17,289,18785,4827745,4948438625,20273753046625,
%T 332185443668950625,21770437421732017110625,
%U 5707011317919939625464790625,5984240806710536532650993759190625
%N a(0)=1, a(1)=4, a(n) = sum_{k=0}^{k=n-1} 4^k a(k).
%F a(n) = (4^(n-2) + 1) * a(n-1). - _Vincenzo Librandi_, Nov 11 2012
%o (Magma) I:=[1, 4, 17]; [n le 3 select I[n] else (4^(n-2)+1)*Self(n-1): n in [1..15]]; // _Vincenzo Librandi, Nov 11 2012
%K nonn,easy
%O 0,2
%A _Olivier Gérard_
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