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A301867
Numbers n such that phi(n), psi(n) and sigma(n) are simultaneously perfect squares.
1
1, 170, 679, 5770, 9154, 9809, 14322, 22413, 37114, 51455, 82615, 100821, 101153, 115430, 139954, 171069, 198462, 222893, 233358, 270485, 349894, 389045, 391090, 514294, 561782, 595122, 608685, 664853, 701338, 815538, 1009527, 1231230, 1290993, 1397091
OFFSET
1,2
COMMENTS
Subsequence of A067781.
The squarefree terms of A067781 are in this sequence (since if n is squarefree then psi(n) = sigma(n)). The nonsquarefree terms of this sequence are: 1, 25264008, 2171889720, 2659240584, 5893922664, 16962447600,...
LINKS
EXAMPLE
170 is in the sequence since phi(170) = 64 = 8^2, sigma(170) = psi(170) = 324 = 18^2.
25264008, the first nonsquarefree term ( > 1 ) in the sequence, has phi = 2520^2, sigma = 9600^2 and psi = 8064^2.
MATHEMATICA
a = {}; psi[n_] := DirichletConvolve[j, MoebiusMu[j]^2, j, n];
aQ[n_] := AllTrue[Sqrt[{DivisorSigma[1, n], EulerPhi[n], psi[n]}], IntegerQ];
Do[If[aQ[k], AppendTo[a, k]], {k, 1, 10^7}]; a
CROSSREFS
Cf. A000010 (phi), A000203 (sigma), A001615 (psi), A067781, A291549.
Sequence in context: A114078 A031704 A173275 * A281397 A206122 A259293
KEYWORD
nonn
AUTHOR
Amiram Eldar, Mar 28 2018
STATUS
approved