A218006 Numbers n such that sigma(tau(phi(n))) = tau(phi(sigma(n))) = phi(sigma(tau(n))).

1, 34, 36, 96, 128, 468, 1200, 21216, 102060, 110976, 117684, 211428, 331380, 366660, 437220, 511680, 530712, 706560, 710388, 726240, 732240, 759360, 838080, 845376, 875840, 911040, 975936, 1014016, 1041216, 1093440, 1110720, 1141440, 1167696, 1289280

Offset: 1

Author

Jayanta Basu, Mar 26 2013

Keywords

• nonn

Comments

Here phi denotes Euler's totient function, tau(n) denotes number of divisors of n and sigma(n) denotes sum of all divisors of n. Only cyclic rotation of operators is considered.

Crossrefs

Cf. A000005, A000010, A000203, A033632, A076361, A078148.

Programs

Mathematica

Select[Range[1000000], DivisorSigma[1, DivisorSigma[0, EulerPhi[#]]] == DivisorSigma[0, EulerPhi[DivisorSigma[1, #]]] == EulerPhi[DivisorSigma[1, DivisorSigma[0, #]]] &]