A214531 List of words over {1,8} with equal numbers of 1's and 8's.

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

Harvey P. Dale, Table of n, a(n) for n = 1..1000

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

Cf. A214218, A214488, A214521, A214522, A214524, A214530.

Sequence in context: A044011 A338039 A085504 * A271502 A235641 A087636

Adjacent sequences: A214528 A214529 A214530 * A214532 A214533 A214534

Keyword

nonn,base,easy

Author

Jonathan Vos Post, Jul 20 2012

Status

approved