A053338 a(n) contains n digits (either '6' or '9') and is divisible by 2^n.
6, 96, 696, 9696, 69696, 669696, 6669696, 96669696, 696669696, 9696669696, 69696669696, 969696669696, 9969696669696, 69969696669696, 969969696669696, 9969969696669696, 99969969696669696, 999969969696669696
Offset: 1
Links
- Ray Chandler, Table of n, a(n) for n = 1..1000
Programs
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Mathematica
Table[Select[FromDigits/@Tuples[{6,9},n],Mod[#,2^n]==0&],{n,20}]//Flatten (* Harvey P. Dale, Sep 15 2023 *)
Formula
a(n)=a(n-1)+10^(n-1)*(6+3*[a(n-1)/2^(n-1) mod 2]) i.e. a(n) ends with a(n-1); if (n-1)-th term is divisible by 2^n then n-th term begins with a 6, if not then n-th term begins with a 9.