OFFSET
0,2
COMMENTS
Hankel transform of A105864.
The sequence 1,1,2,8,... with general term 2^floor(n^2/3) is the Hankel transform of A109033. - Paul Barry, Dec 14 2008
FORMULA
a(n) = 2^floor((n+1)^2/3);
a(n) = Product_{k=1..n} (5/3 - 2*cos(2*Pi*k/3)/3)^(n-k+1);
a(n) = Product_{k=1..n} A130196(k)^(n-k+1).
a(n) = 4*a(n-1)*a(n-3)/a(n-4). Somos-4 sequence associated to, e.g., y^2 = 1 - 8x + 16x^2 - 8x^3. - Paul Barry, Nov 27 2009
a(n) = a(-2-n) for all n in Z. - Michael Somos, May 12 2022
MATHEMATICA
a[ n_] := 2^Quotient[(n+1)^2, 3]; (* Michael Somos, May 12 2022 *)
PROG
(PARI) {a(n) = 2^((n+1)^2\3)}; /* Michael Somos, May 12 2022 */
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paul Barry, Nov 08 2007
STATUS
approved