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A053337
a(n) contains n digits (either '6' or '7') and is divisible by 2^n.
1
6, 76, 776, 7776, 67776, 667776, 6667776, 66667776, 766667776, 6766667776, 66766667776, 666766667776, 7666766667776, 77666766667776, 777666766667776, 7777666766667776, 77777666766667776, 777777666766667776
OFFSET
1,1
LINKS
FORMULA
a(n)=a(n-1)+10^(n-1)*(6+[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 7.
MATHEMATICA
Table[Select[FromDigits/@Tuples[{6, 7}, n], Divisible[#, 2^IntegerLength[ #]]&], {n, 18}]//Flatten (* Harvey P. Dale, Jul 10 2016 *)
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Henry Bottomley, Mar 06 2000
STATUS
approved