a(n) = sigma_7(2n-1).

Terms

a(0) =1a(1) =2188a(2) =78126a(3) =823544a(4) =4785157a(5) =19487172a(6) =62748518a(7) =170939688a(8) =410338674a(9) =893871740a(10) =1801914272a(11) =3404825448a(12) =6103593751a(13) =10465138360a(14) =17249876310a(15) =27512614112a(16) =42637932336a(17) =64340198544a(18) =94931877134a(19) =137293757384a(20) =194754273882a(21) =271818611108a(22) =373845175782