A015495 - OEIS

%I #8 Sep 08 2022 08:44:40

%S 1,7,50,2500,860000,2065720000,34720621760000,4084881150064000000,

%T 3364079361848306816000000,19393251433341842829490432000000,

%U 782587666186514855538867732678656000000

%N a(0)=1, a(1)=7, a(n) = sum_{k=0}^{k=n-1} 7^k a(k).

%F a(n) =  (7^(n-2) + 1) * Self(n-1). - _Vincenzo Librandi_, Nov 11 2012

%o (Magma) I:=[1, 7, 50]; [n le 3 select I[n] else (7^(n-2)+1)*Self(n-1): n in [1..15]]; // _Vincenzo Librandi_, Nov 11 2012

%K nonn,easy

%O 0,2

%A _Olivier Gérard_