OFFSET
1,2
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..1000
EXAMPLE
5 is the smallest integer which does not occur among the first 3 terms of the sequence and which is >= 4. So a(4) = 4 + 5 = 9.
MATHEMATICA
f[l_List] := Block[{n = Length[l] + 1, k = n}, While[MemberQ[l, k], k++ ]; Append[l, n + k]]; Nest[f, {1}, 70] (* Ray Chandler, Oct 09 2006 *)
PROG
(PARI) {m=65; w=vector(3*m); print1(a=1, ", "); for(n=2, m, k=n; while(w[k], k++); print1(a=n+k, ", "); w[a]=1)} \\ Klaus Brockhaus, Oct 09 2006
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Leroy Quet, Oct 08 2006
EXTENSIONS
Corrected and extended by Klaus Brockhaus and Ray Chandler, Oct 09 2006
STATUS
approved