Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #22 Jun 12 2015 10:52:49
%S 69,169,213,341,377,561,671,703,781,897,949,1441,1541,1633,1649,1891,
%T 2001,2201,2701,2769,2873,3053,3201,4061,4331,4371,4899,4901,6001,
%U 6177,6409,6681,7449,7991,9301,9361,11661,12121,12209,12337,12441,12673,12881
%N Pseudoprimes to base 70.
%C Composite numbers n such that 70^(n-1) == 1 (mod n). - _Michel Lagneau_, Feb 18 2012
%H T. D. Noe, <a href="/A020198/b020198.txt">Table of n, a(n) for n = 1..1000</a>
%H <a href="/index/Ps#pseudoprimes">Index entries for sequences related to pseudoprimes</a>
%t base = 70; t = {}; n = 1; While[Length[t] < 100, n++; If[! PrimeQ[n] && PowerMod[base, n-1, n] == 1, AppendTo[t, n]]]; t (* _T. D. Noe_, Feb 21 2012 *)
%t Select[Range[10^4], Not[PrimeQ[#]] && PowerMod[70, # - 1, #] == 1 &] (* _Alonso del Arte_, Jun 12 2015, based on _Farideh Firoozbakht_'s program for A005939 *)
%o (PARI) forcomposite(n=4,1e6, if(Mod(70,n)^(n-1)==1, print1(n", "))) \\ _Charles R Greathouse IV_, Jun 12 2015
%Y Cf. A001567 (pseudoprimes to base 2).
%K nonn
%O 1,1
%A _David W. Wilson_