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Numbers n such that primorial(n)/2 - 64 is prime.
5

%I #11 Apr 11 2017 04:37:07

%S 4,5,6,7,10,13,17,18,28,32,35,38,89,115,117,224,241,353,440,1153,2585,

%T 3075,3456,4895,7483,7649,8197,8625,13285,19849,24179,24442

%N Numbers n such that primorial(n)/2 - 64 is prime.

%C a(33) > 25000. - _Robert Price_, Apr 10 2017

%t k = 1; a = {}; Do[k = k*Prime[n]; If[PrimeQ[k - 64]&&k>64, Print[n]; AppendTo[a, n]], {n, 2, 325}]; a

%t Flatten[Position[Rest[FoldList[Times,1,Prime[Range[600]]]],_?(PrimeQ[ #/2-64]&&#/2>64&)]] (* _Harvey P. Dale_, Mar 05 2013 *)

%t Select[Range[4, 100], PrimeQ[Product[Prime[k], {k, 1, #}]/2 - 64] &] (* _Robert Price_, Apr 10 2017 *)

%Y Cf. A067026, A067027, A139439-A139457, A103514.

%K nonn

%O 1,1

%A _Artur Jasinski_, Apr 21 2008

%E a(18)-a(19) from _Harvey P. Dale_, Mar 05 2013

%E Drop 2 and correct programs, a(20)-a(21) from _Ray Chandler_, Jun 16 2013

%E a(22)-a(32) from _Robert Price_, Apr 10 2017