A047630 Numbers k that divide sigma(k) * phi(k) and are not divisible by 6.

1, 28, 40, 117, 135, 196, 200, 224, 496, 640, 775, 819, 891, 1000, 1372, 1521, 1550, 1568, 1701, 1792, 2176, 2325, 2480, 3100, 3159, 3200, 3375, 3724, 4455, 5000, 5632, 5733, 6200, 6860, 6875, 6975, 8128, 9604, 10240, 10880, 10935, 10976, 11907

Offset

1,2

References

George E. Andrews, "Number Theory," Dover Books, NY, 1971, Page 84.

Links

Harvey P. Dale, Table of n, a(n) for n = 1..483 (* All terms up to 5 million. *)

Mathematica

Do[ If[ Mod[ n, 6 ]!=0, If[ Mod[ DivisorSigma[ 1, n ]*EulerPhi[ n ], n ]==0, Print[ n ] ] ], {n, 1, 25000} ]
Select[Range[12000], Mod[DivisorSigma[1, #]EulerPhi[#], #]==0&&Mod[#, 6]!=0&] (* Harvey P. Dale, Nov 18 2025 *)

Crossrefs

Cf. A011775.

Sequence in context: A383939 A361855 A380073 * A135789 A219882 A154035

Adjacent sequences: A047627 A047628 A047629 * A047631 A047632 A047633

Keyword

easy,nonn

Author

Robert G. Wilson v, Jul 22 2000

Status

approved