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%I #7 Sep 29 2017 17:29:06
%S 0,2,4,8,10,14,18,22,28,36,42,50,56,62,70,80,88,96,104,112,122,134,
%T 144,156,168,180,194,208,220,234,248,262,276,292,308,326,344,362,380,
%U 400,418,438,456,474,494,514,532,550,570,590,612,636,658,682,708,734
%N Number of pairs {i,j} with i different from j; 1<=i<=n; 1<= j <=n such that i+j is a prime number.
%F a(n) = 2 * A071917(n). - _Alois P. Heinz_, Sep 29 2017
%p with(numtheory):
%p b:= proc(n) option remember; `if`(n=0, 0,
%p b(n-1)+pi(2*n-1)-pi(n))
%p end:
%p a:= n-> 2*b(n):
%p seq(a(n), n=1..70); # _Alois P. Heinz_, Sep 29 2017
%t Table[2*Count[Subsets[Range[n],{2}],_?(PrimeQ[Total[#]]&)],{n,50}] (* _Harvey P. Dale_, Jan 23 2015 *)
%Y Partial sums of 2*A060715(n).
%K nonn
%O 1,2
%A _Santi Spadaro_, May 04 2002
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