a(n) = Sum_{d divides n} (-1)^(d + n/d) * d^7.

Terms

a(0) =1a(1) =-129a(2) =2188a(3) =-16257a(4) =78126a(5) =-282252a(6) =823544a(7) =-2080641a(8) =4785157a(9) =-10078254a(10) =19487172a(11) =-35570316a(12) =62748518a(13) =-106237176a(14) =170939688a(15) =-266321793a(16) =410338674a(17) =-617285253a(18) =893871740a(19) =-1270094382a(20) =1801914272a(21) =-2513845188a(22) =3404825448a(23) =-4552442508