A169731 Numbers that are the same upside down (using only digits 0, 1, 6 and 9).

0, 1, 11, 69, 96, 101, 111, 609, 619, 906, 916, 1001, 1111, 1691, 1961, 6009, 6119, 6699, 6969, 9006, 9116, 9696, 9966, 10001, 10101, 11011, 11111, 16091, 16191, 19061, 19161, 60009, 60109, 61019, 61119, 66099, 66199, 69069, 69169, 90006, 90106, 91016, 91116

Offset

1,3

Comments

A000787 without using digit 8, considered here as composed of two circles with different radius. 'Same upside down' means central symmetric, that is 180-degree rotationally symmetric about a central axis perpendicular to the screen plane. See the comment by M. F. Hasler in A000787. - Wolfdieter Lang, Oct 25 2013

Links

Michael S. Branicky, Table of n, a(n) for n = 1..10000 (terms 1..1535 from T. D. Noe)

Prog

(Python)
from itertools import count, islice, product
def ud(s): return s[::-1].translate({ord('6'):ord('9'), ord('9'):ord('6')})
def agen():
    yield from [0, 1]
    for d in count(2):
        for start in "169":
            for rest in product("0169", repeat=d//2-1):
                left = start + "".join(rest)
                right = ud(left)
                for mid in [[""], ["0", "1"]][d%2]:
                    yield int(left + mid + right)
print(list(islice(agen(), 43))) # Michael S. Branicky, Mar 29 2022

Crossrefs

Cf. A000787.

Sequence in context: A066433 A038741 A292490 * A212057 A293550 A182188

Adjacent sequences: A169728 A169729 A169730 * A169732 A169733 A169734

Keyword

nonn,base,easy

Author

N. J. A. Sloane, May 01 2010, based on a suggestion from Terry Stickels

Extensions

Extended by T. D. Noe, May 03 2010

Status

approved