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A015508 a(1)=1, a(n) = sum_{k=1}^{k=n-1} (7^k-1)/6 a(k). 0

%I

%S 1,1,9,522,209322,586520244,11501075464596,1578614616119517768,

%T 1516734501782248791012168,10200952598655696033329019125136,

%U 480252779391204632593567857157274897424,158269444415262012661462389451687149577571916192

%N a(1)=1, a(n) = sum_{k=1}^{k=n-1} (7^k-1)/6 a(k).

%F a(n) = ((7^(n-1) + 5)/6) * a(n-1). - _Vincenzo Librandi_, Nov 12 2012

%o (MAGMA) I:=[1, 1, 9]; [n le 3 select I[n] else ((7^(n-1) + 5)/6) * Self(n-1): n in [1..15]]; // _Vincenzo Librandi_, Nov 12 2012

%K nonn,easy

%O 1,3

%A _Olivier GĂ©rard_

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Last modified August 10 11:03 EDT 2022. Contains 356039 sequences. (Running on oeis4.)