OFFSET
0,4
REFERENCES
D. R. Hofstadter, Goedel, Escher, Bach: an Eternal Golden Braid, Basic Books, 1999, p. 137.
LINKS
David Fifield Table of n, a(n) for n = 0..10000
PROG
(Python) # Emulate a breadth-first traversal of the "flip"
# of the tree defined by the Hofstadter H-sequence.
def hflip_iter():
yield 0
yield 1
# Start on the first node of a left branch, parent node is 1.
queue = [(1, 1)]
n = 2
while True:
parent, state = queue.pop(0)
yield parent
if state == 0:
# Root node. Add the two children.
queue.append((n, 1))
queue.append((n, 0))
elif state == 1:
# First node on left branch. Add the second node.
queue.append((n, 2))
elif state == 2:
# Second node on left branch. Add a new root.
queue.append((n, 0))
n += 1
i = hflip_iter()
for n in range(0, 10001):
print("%d %d" % (n, next(i)))
CROSSREFS
KEYWORD
nonn
AUTHOR
David Fifield, Jan 17 2009
STATUS
approved