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A271839 Somos's sequence {a(9,n)} defined in comment in A018896: a(0)= a(1) = ... = a(19) = 1; for n >= 20, a(n) = (a(n-1)*a(n-19) + a(n-10)^2)/a(n-20).

%I A271839 #25 Feb 16 2025 08:33:33
%S A271839 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2,3,4,5,6,7,8,9,10,11,15,24,
%T A271839 40,65,101,150,214,295,395,911,1479,2164,3105,4571,7033,11252,18383,
%U A271839 30095,48707,141866,372815,816479,1567804,2757573,4585139,7385515
%N A271839 Somos's sequence {a(9,n)} defined in comment in A018896: a(0)= a(1) = ... = a(19) = 1; for n >= 20, a(n) = (a(n-1)*a(n-19) + a(n-10)^2)/a(n-20).
%H A271839 Seiichi Manyama, <a href="/A271839/b271839.txt">Table of n, a(n) for n = 0..555</a>
%H A271839 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/SomosSequence.html">Somos Sequence</a>
%t A271839 a[k_,n_]:=a[k,n]=If[n>2k+1,(a[k,(n-1)]*a[k,(n-2k-1)]+(a[k,(n-k-1)])^2)/a[k,(n-2k-2)],1];
%t A271839 Map[a[9,#]&,Range[0,70]] (* _Peter J. C. Moses_, Apr 15 2016 *)
%o A271839 (PARI) {a(n) = if(n< 20, 1, (a(n-1)*a(n-19) + a(n-10)^2)/a(n-20))};
%o A271839 for(n=0,50, print1(a(n), ", ")) \\ _G. C. Greubel_, Feb 21 2018
%o A271839 (Magma) [n le 20 select 1 else (Self(n-1)*Self(n-19) + Self(n-10)^2 )/Self(n-20): n in [1..50]]; // _G. C. Greubel_, Feb 21 2018
%Y A271839 Cf. A018896, A006125, A006720, A102276, A271341, A271835, A271831, A271837, A271838.
%K A271839 nonn
%O A271839 0,21
%A A271839 _Vladimir Shevelev_ and _Peter J. C. Moses_, Apr 15 2016