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

Author

Robert G. Wilson v, Jul 22 2000

Keywords

• easy
• nonn

References

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

Crossrefs

Cf. A011775.

Programs

Mathematica

Do[ If[ Mod[ n, 6 ]!=0, If[ Mod[ DivisorSigma[ 1, n ]*EulerPhi[ n ], n ]==0, Print[ n ] ] ], {n, 1, 25000} ]