a(n) = Sum_{d|7} phi(d)*n^(7/d).

Terms

a(0) =0a(1) =7a(2) =140a(3) =2205a(4) =16408a(5) =78155a(6) =279972a(7) =823585a(8) =2097200a(9) =4783023a(10) =10000060a(11) =19487237a(12) =35831880a(13) =62748595a(14) =105413588a(15) =170859465a(16) =268435552a(17) =410338775a(18) =612220140a(19) =893871853a(20) =1280000120a(21) =1801088667a(22) =2494358020a(23) =3404825585