login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A083735 Pseudoprimes to bases 3 and 7. 3

%I #21 Jun 29 2019 08:32:53

%S 703,1105,2465,10585,18721,19345,29341,38503,46657,50881,75361,76627,

%T 88831,104653,115921,146611,162401,188191,213265,226801,252601,278545,

%U 286903,294409,314821,334153,340561,359341,385003,385201,399001,410041

%N Pseudoprimes to bases 3 and 7.

%H Amiram Eldar, <a href="/A083735/b083735.txt">Table of n, a(n) for n = 1..16479</a> (terms 1..151 from R. J. Mathar)

%H F. Richman, <a href="http://math.fau.edu/Richman/carm.htm">Primality testing with Fermat's little theorem</a>

%H <a href="/index/Ps#pseudoprimes">Index entries for sequences related to pseudoprimes</a>

%F a(n) = n-th positive integer k(>1) such that 3^(k-1) = 1 (mod k) and 7^(k-1) = 1 (mod k).

%e a(1)=703 since it is the first number such that 3^(k-1) = 1 (mod k) and 7^(k-1) = 1 (mod k).

%t Select[Range[420000],!PrimeQ[#]&&PowerMod[3,#-1,#]==1&&PowerMod[7,#-1,#] == 1&] (* _Harvey P. Dale_, Mar 08 2014 *)

%o (PARI) is(n)=!isprime(n)&&Mod(7,n)^(n-1)==1&&Mod(3,n)^(n-1)==1 \\ _Charles R Greathouse IV_, Apr 12 2012

%Y Intersection of A005935 and A005938. - _R. J. Mathar_, Apr 05 2011

%K nonn

%O 1,1

%A Serhat Sevki Dincer (sevki(AT)ug.bilkent.edu.tr), May 05 2003

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 28 10:55 EDT 2024. Contains 371241 sequences. (Running on oeis4.)