A193167 Composite numbers n such that phi(n) divides 4*(n-1).

4, 6, 8, 10, 12, 15, 28, 66, 91, 561, 946, 6601, 8911, 6840001

Offset

1,1

Links

Table of n, a(n) for n=1..14.

Mathematica

t={}; Do[If[PrimeQ[n]==False && IntegerQ[(n-1)*4/EulerPhi[n]], Print[n]; AppendTo[t, n]], {n, 2, 10^5}]; t
Select[Range[7*10^6], CompositeQ[#]&&Divisible[4(#-1), EulerPhi[#]]&] (* Harvey P. Dale, Jul 07 2016 *)

Prog

(PARI) p=1; forprime(q=2, 1e9, for(n=p+1, q-1, if((4*n-4)%eulerphi(n)==0, print1(n", "))); p=q) \\ Charles R Greathouse IV, Jul 31 2011

Crossrefs

Sequence in context: A286043 A310658 A167179 * A020645 A053226 A227112

Adjacent sequences: A193164 A193165 A193166 * A193168 A193169 A193170

Keyword

nonn

Author

José María Grau Ribas, Jul 20 2011

Status

approved