a(n) = 2*(A056855(n)) /(phi(n)*n), where phi() is the Euler phi function.

Terms

a(0) =2a(1) =1a(2) =1a(3) =1a(4) =5a(5) =1a(6) =84a(7) =11a(8) =184a(9) =15a(10) =193248a(11) =23a(12) =19056960a(13) =833a(14) =33740a(15) =64035a(16) =520105017600a(17) =2473a(19) =203685a(20) =963513600a(21) =23748417a(23) =645119a(25) =8527366575