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%I A015509 #13 May 01 2023 18:02:09
%S A015509 1,1,10,740,433640,2030302480,76034827876000,22779578222682344000,
%T A015509 54596862986901017252624000,1046838176230046602563156976288000,
%U A015509 160576277008444677145920980328106246720000
%N A015509 a(1) = 1, a(n) = Sum_{k=1..n-1} ((8^k - 1)/7)*a(k).
%H A015509 G. C. Greubel, <a href="/A015509/b015509.txt">Table of n, a(n) for n = 1..48</a>
%F A015509 a(n) = ((8^(n-1) + 6)/7) * a(n-1). - _Vincenzo Librandi_, Nov 12 2012
%t A015509 a[n_, m_]:= a[n, m]= If[n<3, 1, (m^(n-1) +m-2)*a[n-1,m]/(m-1)];
%t A015509 Table[a[n,8], {n,30}] (* _G. C. Greubel_, Apr 30 2023 *)
%o A015509 (Magma) [n le 2 select 1 else ((8^(n-1)+6)/7)*Self(n-1): n in [1..15]]; // _Vincenzo Librandi_, Nov 12 2012
%o A015509 (SageMath)
%o A015509 @CachedFunction # a = A015509
%o A015509 def a(n,m): return 1 if (n<3) else (m^(n-1)+m-2)*a(n-1,m)/(m-1)
%o A015509 [a(n,8) for n in range(1,31)] # _G. C. Greubel_, Apr 30 2023
%Y A015509 Sequences with the recurrence a(n) = (m^(n-1) + m-2)*a(n-1)/(m-1): A036442 (m=2),  A015502 (m=3), A015503 (m=4), A015506 (m=5), A015507 (m=6), A015508 (m=7), this sequence (m=8), A015511 (m=9), A015512 (m=10), A015513 (m=11), A015515 (m=12).
%K A015509 nonn,easy
%O A015509 1,3
%A A015509 _Olivier Gérard_

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