OFFSET
1,4
FORMULA
[ C(n+1, 3)/3 ] - [ C(n, 3)/3 ].
G.f.: [x^3(1-x+x^2)(1-x^2+x^3)]/[(1-x)^3(1+x^3+x^6)].
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Ralf Stephan, Oct 24 2003
STATUS
approved