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A372678 a(n) = phi(14 * n)/6. 1
1, 2, 2, 4, 4, 4, 7, 8, 6, 8, 10, 8, 12, 14, 8, 16, 16, 12, 18, 16, 14, 20, 22, 16, 20, 24, 18, 28, 28, 16, 30, 32, 20, 32, 28, 24, 36, 36, 24, 32, 40, 28, 42, 40, 24, 44, 46, 32, 49, 40, 32, 48, 52, 36, 40, 56, 36, 56, 58, 32, 60, 60, 42, 64, 48, 40, 66, 64, 44, 56, 70, 48, 72, 72, 40, 72, 70, 48 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
LINKS
FORMULA
G.f.: Sum_{k>=1} mu(14 * k) * x^k / (1 - x^k)^2, where mu() is the Moebius function (A008683).
Multiplicative with a(p^e) = p^e if p = 2 or 7, and (p-1)*p^(e-1) otherwise.
Sum_{k=1..n} a(k) ~ (49/(12*Pi^2)) * n^2. - Amiram Eldar, May 10 2024
MATHEMATICA
a[n_] := EulerPhi[14 * n]/6; Array[a, 100] (* Amiram Eldar, May 10 2024 *)
PROG
(PARI) a(n) = eulerphi(14*n)/6;
(PARI) my(N=80, x='x+O('x^N)); Vec(sum(k=1, N, moebius(14*k)*x^k/(1-x^k)^2))
CROSSREFS
Column k=14 of A372673.
Cf. A008683.
Sequence in context: A108514 A317419 A364843 * A120456 A367039 A115383
KEYWORD
nonn,mult,easy
AUTHOR
Seiichi Manyama, May 10 2024
STATUS
approved

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Last modified June 28 22:54 EDT 2024. Contains 373816 sequences. (Running on oeis4.)