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%I #28 Jan 30 2018 21:47:41
%S 0,-1,0,0,1,1,1,2,2,1,2,2,3,4,4,3,4,5,5,6,6,5,6,6,7,7,7,7,8,8,8,9,10,
%T 9,10,9,9,10,11,10,11,11,12,13,13,13,14,15,15,15,15,14,15,15,15,15,15,
%U 15,16,17,18,19,20,19,20,19,20,21,21,20,21,22,23,24
%N a(n) = ceiling(n/2) - pi(2n) + pi(n-1).
%C The number of partitions of 2n into exactly two parts such that the first part is an odd composite integer, n > 2.
%H Muniru A Asiru, <a href="/A226983/b226983.txt">Table of n, a(n) for n = 1..1000</a>
%H <a href="/index/Par#part">Index entries for sequences related to partitions</a>
%F a(n) = floor((n+1)/2) - ( pi(2n) - pi(n-1) ) = A004526(n+1) - A035250(n).
%p with(numtheory); seq(ceil(k/2)-(pi(2*k)-pi(k-1)),k=1..100);
%t Table[Floor[(n + 1) / 2] - (PrimePi[2 n] - PrimePi[n - 1]), {n, 100}] (* _Vincenzo Librandi_, Dec 07 2016 *)
%o (PARI) a226983(n) = if(n==1, 0, ceil(n/2) - primepi(2*n) + primepi(n-1)) \\ _Michael B. Porter_, Jun 29 2013
%Y Cf. A000720, A004526, A035250.
%K sign,easy
%O 1,8
%A _Wesley Ivan Hurt_, Jun 25 2013
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