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A214532
List of words over {1,9} with equal numbers of 1's and 9's.
0
19, 91, 1199, 1919, 1991, 9119, 9191, 9911, 111999, 119199, 119919, 119991, 191199, 191919, 191991, 199119, 199191, 199911, 911199, 911919, 911991, 919119, 919191, 919911, 991119, 991191, 991911, 999111, 11119999, 11191999
OFFSET
1,1
COMMENTS
This is to 9 as A214531 is to 8, as A214530 is to 7, as A214530 is to 6, as A214522 is to 5, as A214521 is to 4, as A214488 is to 3, and as A214218 is to 2.
The subsequence of primes (when interpreted as decimal integers) is A087515.
MATHEMATICA
FromDigits/@(Flatten[Permutations/@Table[Join[Table[1, {n}], Table[9, {n}]], {n, 4}], 1]) (* Harvey P. Dale, Aug 20 2014 *)
KEYWORD
nonn,base,easy
AUTHOR
Jonathan Vos Post, Jul 20 2012
STATUS
approved