Search: id:A108894
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%I A108894
%S A108894 0,1,2,11,17,25,38,53,107,245,255,367,719,1077,2189,2853,3236,3511,3633,
%T A108894 4531,4858,5422
%N A108894 Numbers n such that (n!/n#) * 2^n + 1 is prime, where n# = primorial 
               numbers (A034386).
%C A108894 n!/n# is known as n compositorial. All values have been proved prime. 
               No more terms up to 6100. Primality proof for the largest, which 
               has 17219 digits: PFGW Version 1.2.0 for Windows [FFT v23.8] Primality 
               testing (5422!/5422#)*(2^5422)+1 [N-1, Brillhart-Lehmer-Selfridge] 
               Running N-1 test using base 2719 Calling Brillhart-Lehmer-Selfridge 
               with factored part 36.34% (5422!/5422#)*(2^5422)+1 is prime! (66.5095s+0.0129s)
%t A108894 f[n_] := n!/Fold[Times, 1, Prime[ Range[ PrimePi[ n]]]]*2^n + 1; Do[ 
               If[ PrimeQ[ f[n]], Print[n]], {n, 0, 1100}] (from Robert G. Wilson 
               v (rgwv(AT)rgwv.com), Jul 18 2005)
%Y A108894 Cf. A049420, A091421.
%Y A108894 Sequence in context: A156829 A105840 A060427 this_sequence A066794 A153222 
               A087379
%Y A108894 Adjacent sequences: A108891 A108892 A108893 this_sequence A108895 A108896 
               A108897
%K A108894 more,nonn
%O A108894 1,3
%A A108894 Jason Earls (zevi_35711(AT)yahoo.com), Jul 15 2005

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