OFFSET
1,1
FORMULA
a(n) = 2^b(n) and {b(n)}={1, 3, 4, 4, 6, 7, 7, 9, 10, 10, 12, 13, 13, 15, ..} where b(3n-2)=3n-2, b(3n-1)=3n, b(3n)=b(3n+1)=3n+1, for n>0.
PROG
(PARI) apply(n->2^n, Vec((1+2*x+x^2-x^3)/(1-x-x^3+x^4)+O(x^30))) \\ Charles R Greathouse IV, Apr 09 2012
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Benoit Cloitre and Paul D. Hanna, Jan 28 2003
STATUS
approved