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%I #15 Jul 18 2014 11:00:00
%S 4,5,7,8,10,11,13,14,16,17,18,20,22,23,25,26,28,29,31,32,33,35,37,38,
%T 39,41,43,44,46,47,48,50,52,53,55,56,58,59,60,61,62,63,65,67,68,70,71,
%U 72,73,74,76,77,78,80,81,83,85,86,88,89,91,92,93,94,95,97
%N a(n) is smallest number greater than a(n-1) such that a(n)+a(n-1) is composite.
%H Harvey P. Dale, <a href="/A231507/b231507.txt">Table of n, a(n) for n = 1..1000</a>
%e a(1) = 4, the first composite. So the smallest a(2) could possibly be 5. 4+5=9, which is composite, so a(2) = 5. a(3) cannot be 6, because 5+6=11, which is prime. But 5+7=12 is composite, so a(3) = 7.
%t nxt[n_]:=Module[{k=n+1},While[PrimeQ[n+k],k++];k]; NestList[nxt,4,70] (* _Harvey P. Dale_, Jul 18 2014 *)
%Y Cf. A062042, A073627.
%K nonn
%O 1,1
%A _Neil Fernandez_, Nov 09 2013
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