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