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%I #16 Feb 09 2018 03:26:32
%S 1,0,0,0,0,0,0,0,1,1,1,1,1,1,2,2,2,2,2,2,3,3,3,3,4,4,5,5,5,5,5,5,6,6,
%T 7,7,7,7,8,8,8,8,8,8,9,9,9,9,10,10,11,11,11,11,12,12,13,13,13,13,13,
%U 13,14,14,15,15,15
%N a(n) = ceiling(n/2) - primepi(n).
%C The number of partitions of 2n into exactly two parts such that the smaller part is an odd composite integer, n > 1.
%C Sequence decreases by 1 when n is an even prime and increases by 1 when n is an odd composite. - _Wesley Ivan Hurt_, Dec 27 2013
%H <a href="/index/Par#part">Index entries for sequences related to partitions</a>
%F a(n) = floor((n+1)/2) - pi(n) = A004526(n+1) - A000720(n).
%F a(n) = n - A004526(n) - A000720(n). - _Wesley Ivan Hurt_, Dec 27 2013
%e a(18) =2. 2*18=38 has two partitions into exactly two odd parts with smallest part composite: (27,9) and (21,15). - _Wesley Ivan Hurt_, Dec 27 2013
%p seq(ceil(n/2)-numtheory[pi](n),n=1..100);
%Y Cf. A000720, A004526, A002375, A141100.
%K nonn,easy
%O 1,15
%A _Wesley Ivan Hurt_, Jun 25 2013
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