OFFSET
1,1
COMMENTS
As A033627, but first term is 2.
4 and the numbers in A047243. - Joerg Arndt, Jun 22 2014
LINKS
FORMULA
a(2n) = 6(n-1)+2 & a(2n+1) = 6(n-1)+3 for n>1. - Robert G. Wilson v, Jun 23 2014
From Colin Barker, Jun 26 2014: (Start)
a(n) = a(n-1) + a(n-2) - a(n-3) for n > 6.
G.f.: x*(x^5 + 3*x^3 - x^2 + x + 2)/((x - 1)^2*(x + 1)). (End)
E.g.f.: (x^3 + 3*x^2 + 30*x + 24)/6 + (3*x - 4)*cosh(x) + 3*(x - 2)*sinh(x). - Stefano Spezia, Apr 15 2023
MATHEMATICA
f[s_List] := Block[{k = s[[-1]] + 1, ss = Union[Plus @@@ Subsets[s, {2}]]}, While[ MemberQ[ss, k], k++]; Append[s, k]]; Nest[f, {2}, 70] (* Robert G. Wilson v, Jun 23 2014 *)
PROG
(PARI) Vec(x*(x^5+3*x^3-x^2+x+2)/((x-1)^2*(x+1)) + O(x^100)) \\ Colin Barker, Jun 26 2014
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Leonardo Sznajder, Jun 21 2014
EXTENSIONS
Added terms >= 20, Joerg Arndt, Jun 22 2014
STATUS
approved