Search: id:A103787
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%I A103787
%S A103787 1,2,4,8,12,21,40,70,117,263,450,703,1385,2423,5501,8617,18249,29352,
%T A103787 61970,103568,209309,404977
%N A103787 a(n) = number of k's that make primorial P(n)/A019565(k)+A019565(k) prime, 
               A019565(k)^2<=P(n).
%C A103787 If we remove the restriction A019565(k)^2<=P(n), every elements get doubled.
%e A103787 P(1)=2, A019565(0)=1, 2/1+1=3 is prime, a(1)=1;
%e A103787 P(2)=6, A019565(0)=1, 6/1+1=7; A019565(1)=2, 6/2+2=5; so, a(2)=2;
%t A103787 npd = 1; Do[npd = npd*Prime[n]; tn = 0; tt = 1; cp = npd/tt + tt; ct 
               = 0; While[IntegerQ[cp], If[(cp >= (tt*2)) && PrimeQ[cp], ct = ct 
               + 1]; tn = tn + 1; tt = 1; k1 = tn; o = 1; While[k1 > 0, k2 = Mod[k1, 
               2]; If[k2 == 1, tt = tt*Prime[o]]; k1 = (k1 - k2)/2; o = o + 1]; 
               cp = npd/tt + tt]; Print[ct], {n, 1, 22}]
%Y A103787 Cf. A019565, A002110, A103785, A103786.
%Y A103787 Sequence in context: A076651 A081410 A027677 this_sequence A032473 A084422 
               A089821
%Y A103787 Adjacent sequences: A103784 A103785 A103786 this_sequence A103788 A103789 
               A103790
%K A103787 hard,nonn
%O A103787 1,2
%A A103787 Lei Zhou (lzhou5(AT)emory.edu), Feb 15 2005

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