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A214531
List of words over {1,8} with equal numbers of 1's and 8's.
2
18, 81, 1188, 1818, 1881, 8118, 8181, 8811, 111888, 118188, 118818, 118881, 181188, 181818, 181881, 188118, 188181, 188811, 811188, 811818, 811881, 818118, 818181, 818811, 881118, 881181, 881811, 888111
OFFSET
1,1
COMMENTS
This 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. All of these, interpreted as decimal integers are divisible by 9, because each pair of "1" and "8" contributes a digital sum of 9, hence the total is divisible by 9.
LINKS
MATHEMATICA
With[{tb=Table[Join[PadRight[{}, n, 1], PadRight[{}, n, 8]], {n, 3}]}, FromDigits/@ Flatten[Permutations/@tb, 1]] (* Harvey P. Dale, Jan 17 2014 *)
CROSSREFS
KEYWORD
nonn,base,easy
AUTHOR
Jonathan Vos Post, Jul 20 2012
STATUS
approved