OFFSET
1,2
COMMENTS
Eric Angelini's definition was: start with 1,2,3; then alternately adjoin either the sum of the last two terms or the smallest number not yet in the sequence.
LINKS
M. F. Hasler, Table of n, a(n) for n = 1..2001
PROG
(PARI) f="b156031.txt"; used=[]; write(f, c=1, " ", b=1); a=1; for(i=1, 1e3, used=setunion(used, Set(a+=b)); while(setsearch(used, b++), used=setminus(used, Set(b))); write(f, c++, " "a"\n", c++, " "b)) \\ M. F. Hasler, Nov 01 2009
(Haskell)
import Data.List (transpose)
a156031 n = a156031_list !! n
a156031_list = tail $ concat (transpose [a022941_list, a143344_list])
-- Reinhard Zumkeller, May 17 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Nov 01 2009, based on a posting by Eric Angelini to the Sequence Fans Mailing List
STATUS
approved