OFFSET
1,2
COMMENTS
Essentially the same sequence as A047231. - Stefan Steinerberger, Oct 17 2008
LINKS
Index entries for linear recurrences with constant coefficients, signature (1, 0, 1, -1).
FORMULA
G.f.: x(1+x)(1+x^2-x^3+2x^4)/((1+x+x^2)(1-x)^2). a(n)=a(n-3)+6, n>5. a(n) = 2n -11/3 +A099837(n+3)/3, n>2. [From R. J. Mathar, Oct 15 2008]
MATHEMATICA
Join[{1, 2}, LinearRecurrence[{1, 0, 1, -1}, {3, 4, 6, 9}, 100]] (* or *) nxt[ {a_, b_, c_}]:= {c+1, c+3, c+6}; Flatten[NestList[nxt, {1, 2, 3}, 30]] (* Harvey P. Dale, Nov 23 2012 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Milton L. Brown (miltbrown(AT)earthlink.net), Oct 13 2008
EXTENSIONS
Extended by R. J. Mathar, Oct 15 2008
STATUS
approved