%I #11 Sep 08 2022 08:45:49

%S 1,1,3,27,243,6561,531441,43046721,10460353203,7625597484987,

%T 5559060566555523,12157665459056928801,79766443076872509863361,

%U 523347633027360537213511521,10301051460877537453973547267843

%N a(n) = 3^floor(n^2/3).

%C Hankel transform of A168494. Trivial Somos-4 sequence linked to elliptic curve y^2=1-10x+25x^2-12x^3.

%H Vincenzo Librandi, <a href="/A168495/b168495.txt">Table of n, a(n) for n = 0..79</a>

%F a(n) = 9*a(n-1)*a(n-3)/a(n-4).

%t Table[3^Floor[n^2/3], {n,0,20}] (* _G. C. Greubel_, Sep 18 2018 *)

%o (Magma) [3^Floor(n^2/3): n in [0..15]]; // _Vincenzo Librandi_, Sep 15 2011

%o (PARI) vector(20, n, n--; 3^floor(n^2/3)) \\ _G. C. Greubel_, Sep 18 2018

%K nonn,easy

%O 0,3

%A _Paul Barry_, Nov 27 2009