OFFSET
1,2
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
15 is in the sequence because Jacobsthal numbers 3 and 5 multiply to 15.
MAPLE
N:= 10000: # to get all terms <= N
J:= gfun:-rectoproc({a(n)=a(n-1)+2*a(n-2), a(0)=0, a(1)=1}, a(n), remember):
P:= {1};
for j from 3 to ilog2(N*3+1) do
x:= J(j);
P:= `union`(seq(select(`<=`, map(`*`, P, x^k), N), k=0..floor(log[x](N))))
od:
sort(convert(P, list)); # Robert Israel, Nov 19 2015
MATHEMATICA
max = 11; jacobProds = Table[(2^n - (-1)^n)/3, {n, 2, max]; curr = 2; While[jacobProds[[curr]] < 2^max/3, jacobProds = Union[jacobProds, jacobProds[[curr]] * jacobProds]; curr++]; Select[jacobProds, # < 2^max/3 &] (* Alonso del Arte, Nov 18 2015 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Jeffrey Shallit, Nov 18 2015
STATUS
approved