OFFSET
1,3
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
EXAMPLE
n=21: '11'*'111' -> '10'*'11' -> '11'*'1' -> '1'; i.e., 21=3*7 -> 6=2*3 -> 2*1 -> 1*1=1, therefore a(21)=3.
MAPLE
A072086 := proc(n) local c, i, j; c :=0; i := n;
while i > 1 do i:=A072084(i); c:=c+1 od; c end:
# Note that this gives A072086(0)=0 if desired
# without any additional case discrimination.
# Peter Luschny, Jan 16 2010
MATHEMATICA
b[1] = 1; b[n_] := Times @@ Power @@@ (FactorInteger[n] /. {p_Integer, e_} :> {DigitCount[p, 2, 1], e}); a[n_] := Length[FixedPointList[b, n]] - 2; Array[a, 100] (* Jean-François Alcover, Feb 09 2018 *)
PROG
(Haskell)
a072086 n = fst $
until ((== 1) . snd) (\(i, x) -> (i + 1, a072084 x)) (0, n)
-- Reinhard Zumkeller, Feb 10 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Jun 14 2002
STATUS
approved