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

Author

Jonathan Vos Post, Jul 20 2012

Keywords

• nonn
• base
• easy

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

Crossrefs

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

Programs

Mathematica

With[{tb=Table[Join[PadRight[{},n,1],PadRight[{},n,8]],{n,3}]},FromDigits/@ Flatten[Permutations/@tb,1]] (* Harvey P. Dale, Jan 17 2014 *)