A066670 Primes arising in A066669: the only odd prime divisor of phi(A066669(n)).

3, 3, 5, 3, 3, 3, 3, 5, 11, 5, 3, 3, 7, 5, 3, 3, 3, 5, 3, 5, 3, 11, 23, 5, 3, 13, 5, 3, 7, 29, 3, 5, 11, 3, 3, 5, 3, 5, 41, 3, 7, 5, 11, 3, 11, 23, 3, 5, 3, 3, 13, 53, 5, 3, 7, 11, 7, 29, 3, 5, 3, 5, 17, 11, 3, 23, 3, 7, 37, 5, 3, 3, 13, 5, 5, 41, 83, 3, 43, 7, 5, 29, 11, 89, 3, 11, 5, 23, 3, 3

Offset: 1

Author

Labos Elemer, Dec 18 2001

Keywords

• nonn

Examples

			A066669(9) = 23, phi(23) = 2*11, so a(9)=11.
		

Links

• Michael De Vlieger, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000010, A000265, A053575, A006530, A065966, A066669, A066671, A066672, A066673.

Programs

Mathematica

Select[Array[#/2^IntegerExponent[#, 2] &@ EulerPhi@ # &, 200], PrimeQ]  (* Michael De Vlieger, Dec 08 2018 *)

PARI

lista(nn) = {for (n=1, nn, en=eulerphi(n); if (isprime(p=en>>valuation(en, 2)), print1(p, ", ")); ); } \\ Michel Marcus, Dec 08 2018

Formula

From Amiram Eldar, Jul 18 2024: (Start)

a(n) = A053575(A066669(n)).

a(n) = A000265(A000010(A066669(n))) = A006530(A000010(A066669(n))). (End)