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%I #6 Mar 30 2012 17:22:25
%S 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,2,0,0,0,1,
%T 0,0,0,0,0,0,0,1,0,0,0,1,2,1,1,0,0,0,1,1,1,1,0,0,0,0,1,2,0,0,0,2,2,2,
%U 1,0,0,1,1,1,1,0,1,0,1,1,0,1,0,0,0,0,1,0,0,0,1,1,0,1,0,0,1,0,2,2,2,1,1,0,0
%N Number of even numbers that cannot be expressed as the difference p-q of two odd primes q < p <= prime(n).
%C If a(n)=0, then Prime[n], called a cluster prime, is in A038134. If a(n)>0 then Prime[n] is in A038133.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/ClusterPrime.html">Cluster Primes</a>
%e a(25)=1 because Prime[25]=97 and there is 1 even number, 88, that cannot be written as the difference of two odd primes less than or equal to 97.
%t m=10000; n=PrimePi[m]-1; p=Table[Prime[i+1], {i, n}]; d=Table[0, {m/2}]; c=Table[0, {n}]; For[i=2, i<=n, i++, For[j=1, j<i, j++, diff=p[[i]]-p[[j]]; d[[diff/2]]++ ]; c[[i]]=Count[Take[d, (p[[i]]-3)/2], 0]]; c
%Y Cf. A038133, A038134.
%K easy,nonn
%O 2,30
%A _T. D. Noe_, Jul 15 2002, Nov 19 2006
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