login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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 (list; graph; refs; listen; history; text; internal format)
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
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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified April 22 06:34 EDT 2024. Contains 371887 sequences. (Running on oeis4.)