Search: id:A071917
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%I A071917
%S A071917 0,1,2,4,5,7,9,11,14,18,21,25,28,31,35,40,44,48,52,56,61,67,72,78,84,
%T A071917 90,97,104,110,117,124,131,138,146,154,163,172,181,190,200,209,219,228,
%U A071917 237,247,257,266,275,285,295,306,318,329,341,354,367,381,395,408,421
%N A071917 Number of pairs (x,y) where x is even, y is odd, 1<=x<=n, 1<=y<=n and 
               x+y is prime.
%F A071917 a(n) = sum over primes p from 3 to 2n-1 of min(p-1, 2n+1-p)/2.
%e A071917 a(6)=7: The sums x+y are 2+1, 2+3, 2+5, 4+1, 4+3, 6+1, 6+5.
%t A071917 a[n_] := Sum[If[PrimeQ[p], Min[p-1, 2n+1-p]/2, 0], {p, 3, 2n-1}]
%Y A071917 Sequence in context: A057352 A156625 A058577 this_sequence A051060 A116650 
               A140205
%Y A071917 Adjacent sequences: A071914 A071915 A071916 this_sequence A071918 A071919 
               A071920
%K A071917 easy,nonn
%O A071917 1,3
%A A071917 Enoch Haga (Enokh(AT)comcast.net), Jun 13 2002
%E A071917 Edited by Dean Hickerson (dean.hickerson(AT)yahoo.com), Jun 18 2002

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