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A230224 Number of ways to write 2*n = p + q + r + s with p <= q <= r <= s such that p, q, r, s are primes in A230223.

%I A230224 #7 Oct 12 2013 01:44:18
%S A230224 0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,1,0,1,1,2,1,2,1,2,2,4,1,3,3,3,4,4,3,5,
%T A230224 4,5,3,6,4,6,5,5,5,7,5,9,4,6,6,8,6,9,5,7,7,10,6,8,7,8,7,9,5,10,7,11,7,
%U A230224 7,7,11,7,10,6,10,6,13,7,9,7,11,9,11,7,9,6,14,8,12,6,13,11,12,11,13,10,16,9,14,7,14
%N A230224 Number of ways to write 2*n = p + q + r + s with p <= q <= r <= s such that p, q, r, s are primes in A230223.
%C A230224 Conjecture: a(n) > 0 for all n > 17.
%H A230224 Zhi-Wei Sun, <a href="/A230224/b230224.txt">Table of n, a(n) for n = 1..3000</a>
%H A230224 Zhi-Wei Sun, <a href="http://arxiv.org/abs/1211.1588">Conjectures involving primes and quadratic forms</a>, preprint, arXiv:1211.1588.
%e A230224 a(21) = 1 since 2*21 = 7 + 7 + 11 + 17, and 7, 11, 17 are primes in A230223.
%e A230224 a(27) = 1 since 2*27 = 7 + 11 + 17 + 19, and 7, 11, 17, 19 are primes in A230223.
%t A230224 RQ[n_]:=n>5&&PrimeQ[3n-4]&&PrimeQ[3n-10]&&PrimeQ[3n-14]
%t A230224 SQ[n_]:=PrimeQ[n]&&RQ[n]
%t A230224 a[n_]:=Sum[If[RQ[Prime[i]]&&RQ[Prime[j]]&&RQ[Prime[k]]&&SQ[2n-Prime[i]-Prime[j]-Prime[k]],1,0],
%t A230224 {i,1,PrimePi[n/2]},{j,i,PrimePi[(2n-Prime[i])/3]},{k,j,PrimePi[(2n-Prime[i]-Prime[j])/2]}]
%t A230224 Table[a[n],{n,1,100}]
%Y A230224 Cf. A002375, A068307, A230223, A230140, A230141, A230219.
%K A230224 nonn
%O A230224 1,20
%A A230224 _Zhi-Wei Sun_, Oct 12 2013