

A169731


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


4



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
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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 180degree 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



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//21):
left = start + "".join(rest)
right = ud(left)
for mid in [[""], ["0", "1"]][d%2]:
yield int(left + mid + right)


CROSSREFS



KEYWORD

nonn,base,easy


AUTHOR



EXTENSIONS



STATUS

approved



