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A053333
a(n) contains n digits (either '4' or '9') and is divisible by 2^n.
1
4, 44, 944, 4944, 94944, 994944, 4994944, 94994944, 494994944, 9494994944, 49494994944, 449494994944, 9449494994944, 99449494994944, 499449494994944, 9499449494994944, 49499449494994944, 949499449494994944
OFFSET
1,1
LINKS
FORMULA
a(n)=a(n-1)+10^(n-1)*(4+5*[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 4, if not then n-th term begins with a 9.
MATHEMATICA
nxt[{n_, a_}]:=Module[{fd=If[Mod[a, 2^(n+1)]==0, 4, 9]}, {n+1, fd 10^IntegerLength[a]+a}]; NestList[ nxt, {1, 4}, 20][[;; , 2]] (* Harvey P. Dale, Jul 14 2023 *)
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Henry Bottomley, Mar 06 2000
STATUS
approved