Pillai's arithmetical function: Sum_{k=1..n} gcd(k, n).

Terms

a(0) =1a(1) =3a(2) =5a(3) =8a(4) =9a(5) =15a(6) =13a(7) =20a(8) =21a(9) =27a(10) =21a(11) =40a(12) =25a(13) =39a(14) =45a(15) =48a(16) =33a(17) =63a(18) =37a(19) =72a(20) =65a(21) =63a(22) =45a(23) =100a(24) =65a(25) =75a(26) =81a(27) =104a(28) =57a(29) =135