OFFSET
1,3
COMMENTS
REFERENCES
M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, 1964 (and various reprintings), p. 840.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
for n = 13, the number 7 is in the sequence because :
f(13) = 13 - phi(tau(13)) = 13 - phi(2) = 13 - 1 = 12;
f(12) = 12 - phi(tau(12)) = 12 - phi(6) = 12 - 2 = 10;
f(10) = 10 - phi(tau(10)) = 10 - phi(4) = 10 - 2 = 8;
f(8) = 8- phi(tau(8)) = 8 - phi(4) = 8 - 2 = 6 ;
f(6) = 6- phi(tau(6)) = 6 - phi(4) = 6 - 2 = 4 ;
f(4) = 4- phi(tau(4)) = 4 - phi(3) = 4 - 2 = 2 ;
f(2) = 2- phi(tau(2)) = 2 - phi(2) = 2 - 1 = 1, and a(13) = 7.
MAPLE
with(numtheory): n0:=200:tabl:=array(1..n0): for n from 1 to 1000 do:k:=0:nn:=n:for q from 0 to 1000 while(nn<>1) do:nn:=nn - phi(tau((nn))):k:=k+1:od:tabl[n]:=k:od:print(tabl):
MATHEMATICA
f[n_] := (k++; n - EulerPhi[ DivisorSigma[0, n]]); f[0] = 0; a[n_] := (k=0; FixedPoint[f, n]; k-1); Table[a[n], {n, 1, 76}](* Jean-François Alcover, May 10 2012 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Apr 27 2010
STATUS
approved