Bisection of A001157: sigma_2(2n).

Terms

a(0) =5a(1) =21a(2) =50a(3) =85a(4) =130a(5) =210a(6) =250a(7) =341a(8) =455a(9) =546a(10) =610a(11) =850a(12) =850a(13) =1050a(14) =1300a(15) =1365a(16) =1450a(17) =1911a(18) =1810a(19) =2210a(20) =2500a(21) =2562a(22) =2650a(23) =3410a(24) =3255a(25) =3570a(26) =4100a(27) =4250a(28) =4210a(29) =5460