Bisection of A001157: a(n) = sigma_2(2n-1).

Terms

a(0) =1a(1) =10a(2) =26a(3) =50a(4) =91a(5) =122a(6) =170a(7) =260a(8) =290a(9) =362a(10) =500a(11) =530a(12) =651a(13) =820a(14) =842a(15) =962a(16) =1220a(17) =1300a(18) =1370a(19) =1700a(20) =1682a(21) =1850a(22) =2366a(23) =2210a(24) =2451a(25) =2900a(26) =2810a(27) =3172a(28) =3620a(29) =3482