The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Please make a donation to keep the OEIS running. We are now in our 56th year. In the past year we added 10000 new sequences and reached almost 9000 citations (which often say "discovered thanks to the OEIS"). Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A227180 Composite numbers n such that b^(n-1) == 1 (mod n) implies b == -1 or +1 (mod n). 2
 4, 6, 8, 9, 10, 12, 14, 16, 18, 20, 22, 24, 26, 27, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 54, 56, 58, 60, 62, 64, 68, 72, 74, 78, 80, 81, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 104, 106, 108, 110, 114, 116, 118, 120, 122, 126, 128, 132, 134, 136, 138, 140, 142, 144, 146, 150, 152, 156, 158, 160, 162, 164, 166, 168, 170 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The sequence is the union of A111305 with {3^k | k > 1}. The composite numbers not in this sequence are the Fermat pseudoprimes A181780. LINKS MATHEMATICA FQ[k_]:= Block[{}, GCD[EulerPhi[k], k-1]==1||IntegerQ[Log[3, k]]]; Select[Range[4, 170], FQ] PROG (PARI) is(n)=for(b=2, n-2, if(Mod(b, n)^(n-1)==1, return(0))); !isprime(n) \\ Charles R Greathouse IV, Dec 22 2016 CROSSREFS Cf. A111305, A181780, A209211. Sequence in context: A327776 A102554 A070810 * A129930 A128510 A109289 Adjacent sequences:  A227177 A227178 A227179 * A227181 A227182 A227183 KEYWORD nonn AUTHOR Emmanuel Vantieghem, Jul 03 2013 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 4 12:33 EST 2020. Contains 338923 sequences. (Running on oeis4.)