OFFSET
0,3
EXAMPLE
S_0 = [1]
S_1 = [0,1,2]
S_2 = [1,0,1,0,1,2,1,2,3]
S_3 = [0,1,2,1,0,1,0,1,2,1,0,1,0,1,2,1,2,3,0,1,2,1,2,3,2,3,4]
etc.
MATHEMATICA
Nest[ Flatten[ # /. a_Integer -> {Abs[a - 1], a, a + 1}] &, {1}, 5]
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Apr 05 2009
EXTENSIONS
Edited by N. J. A. Sloane, Apr 07 2009
STATUS
approved