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A065154
Numbers for which the cototient of the totient is strictly less than the totient of the cototient.
3
2, 6, 12, 15, 24, 30, 48, 51, 60, 66, 70, 78, 90, 96, 102, 105, 120, 130, 132, 138, 140, 150, 154, 156, 165, 170, 174, 180, 190, 192, 204, 210, 230, 234, 238, 240, 246, 255, 260, 264, 266, 270, 276, 280, 282, 290, 300, 308, 312, 315, 318, 330, 340, 345, 348
OFFSET
1,1
LINKS
FORMULA
Numbers n such that phi(n) - phi(phi(n)) < phi(n - phi(n)) or A051953(A000010(n)) < A000010(A051953(n)).
EXAMPLE
Since phi(78) = 24, 78 - phi(78) = cototient(78) = 54, phi(54) = 18. On the other hand, cototient(24) = 24 - phi(24) = 24 - 8 = 16, and because 16 < 18, 78 is a term of this sequence.
MATHEMATICA
co[n_] := n - EulerPhi[n]; Select[Range[400], co[EulerPhi[#]] < EulerPhi[ co[#]] &] (* Harvey P. Dale, May 29 2013 *)
Select[Range[400], EulerPhi[#] - EulerPhi[EulerPhi[#]] < EulerPhi[# - EulerPhi[#]] &] (* Alonso del Arte, Jun 12 2013 *)
PROG
(PARI) { n=0; for (m = 2, 10^9, t=eulerphi(m); c=m - t; if (t - eulerphi(t) < eulerphi(c), write("b065154.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, Oct 13 2009
CROSSREFS
Sequence in context: A334308 A242336 A285312 * A354757 A230482 A263546
KEYWORD
nonn
AUTHOR
Labos Elemer, Oct 19 2001
STATUS
approved