OFFSET
0,3
COMMENTS
a(n) is the determinant of the symmetric matrix (if(j<=floor((i+j)/2), 2^j*F(j+1), 2^i*F(i+1)))_{0<=i,j<=n}.
FORMULA
a(n) = Product_{k=0..n} (1+sqrt(5))^k/2+(1-sqrt(5))^k/2.
a(n) = Product_{k=0..n} Sum_{j=0..floor(k/2)} binomial(n,2k)*5^k}.
a(n) ~ c * (1+sqrt(5))^(n*(n+1)/2) / 2^(n+1), where c = A218490 = 1.3578784076121057013874397... is the Lucas factorial constant. - Vaclav Kotesovec, Jul 11 2015
EXAMPLE
a(2)=6 since det[1, 1, 1; 1, 2, 2; 1, 2, 8]=6.
MATHEMATICA
Table[FullSimplify[Product[(1+Sqrt[5])^k/2 + (1-Sqrt[5])^k/2, {k, 0, n}]], {n, 0, 15}] (* Vaclav Kotesovec, Jul 11 2015 *)
Table[Product[LucasL[k]*2^(k-1), {k, 0, n}], {n, 0, 15}] (* Vaclav Kotesovec, Jul 11 2015 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Paul Barry, Feb 16 2011
STATUS
approved