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A154951 Found by taking the tree defined by the Hofstadter H-sequence (A005374), mirroring it left to right and relabeling the nodes so they increase left to right. a(n) is the parent node of node n in the tree so constructed. 1
0, 1, 1, 2, 3, 4, 4, 5, 6, 6, 7, 8, 9, 9, 10, 10, 11, 12, 13, 13, 14, 15, 15, 16, 16, 17, 18, 19, 19, 20, 21, 22, 22, 23, 24, 24, 25, 25, 26, 27, 28, 28, 29, 29, 30, 31, 32, 32, 33, 34, 35, 35, 36, 37, 37, 38, 38, 39, 40, 41, 41, 42, 43, 43, 44, 44, 45, 46, 47, 47 (list; graph; refs; listen; history; text; internal format)
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

Cf. A005374, A123070.

Sequence in context: A249569 A094500 A049473 * A095769 A080820 A274687

Adjacent sequences:  A154948 A154949 A154950 * A154952 A154953 A154954

KEYWORD

nonn

AUTHOR

David Fifield, Jan 17 2009

STATUS

approved

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Last modified May 7 17:52 EDT 2021. Contains 343652 sequences. (Running on oeis4.)