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A225679
Numerators of phi(k)/k, as k runs through the squarefree numbers (A005117).
4
1, 1, 2, 4, 1, 6, 2, 10, 12, 3, 8, 16, 18, 4, 5, 22, 6, 28, 4, 30, 20, 8, 24, 36, 9, 8, 40, 2, 42, 11, 46, 32, 52, 8, 12, 14, 58, 60, 15, 48, 10, 66, 44, 12, 70, 72, 18, 60, 4, 78, 20, 82, 64, 21, 56, 88, 72, 20, 23, 72, 96, 100, 16, 102, 16, 26, 106, 108, 4
OFFSET
1,3
COMMENTS
To every fraction taken by the arithmetical function m -> phi(m)/m there is exactly one n such that a(n)/A225680(n) is equal to it.
LINKS
FORMULA
a(n) = A000010(A005117(n))/gcd(A000010(A005117(n)),A005117(n)).
Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=1..m} a(k)/A225680(k) = Product_{p prime} (1 - 1/(p*(p+1))) = 0.7044422... (A065463). - Amiram Eldar, Nov 21 2022
EXAMPLE
A005117(5) = 6, phi(6)/6 = 2/6 = 1/3, so a(5) = 1.
MATHEMATICA
s = Select[Range[200], SquareFreeQ]; Numerator[EulerPhi[s]/s] (* T. D. Noe, May 13 2013 *)
PROG
(PARI) lista(nn) = apply(x->(numerator(eulerphi(x)/x)), Vec(select(issquarefree, [1..nn], 1))); \\ Michel Marcus, Feb 22 2021
CROSSREFS
Cf. A000010, A005117, A065463, A225680 (denominators).
Sequence in context: A096907 A360555 A249146 * A375494 A081879 A066248
KEYWORD
nonn,frac,easy
AUTHOR
Franz Vrabec, May 12 2013
STATUS
approved