Number of subsets of A = {1,2,...,n} that have the same center of gravity as A, i.e., (n+1)/2.

Terms

a(0) =1a(1) =1a(2) =3a(3) =3a(4) =7a(5) =7a(6) =19a(7) =17a(8) =51a(9) =47a(10) =151a(11) =137a(12) =471a(13) =427a(14) =1519a(15) =1391a(16) =5043a(17) =4651a(18) =17111a(19) =15883a(20) =59007a(21) =55123a(22) =206259a(23) =193723a(24) =729095a(25) =688007a(26) =2601639a(27) =2465133a(28) =9358943a(29) =8899699