Number of nonempty subsets of {1,2,...,n} in which exactly 1/4 of the elements are <= (n-4)/2.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =10a(6) =20a(7) =41a(8) =77a(9) =126a(10) =252a(11) =392a(12) =844a(13) =1270a(14) =2800a(15) =4070a(16) =9020a(17) =12782a(18) =28679a(19) =40022a(20) =91286a(21) =126048a(22) =291018a(23) =398125a(24) =926177a(25) =1256717a(26) =2942192a(27) =3965620a(28) =9343948a(29) =12526280