a(n) = Sum_{k=1..n-1} gcd(k,n)*a(k), a(1) = 1.

Terms

a(0) =1a(1) =1a(2) =2a(3) =5a(4) =9a(5) =28a(6) =46a(7) =136a(8) =288a(9) =722a(10) =1238a(11) =4342a(12) =6818a(13) =19146a(14) =45026a(15) =111698a(16) =189506a(17) =624930a(18) =1003942a(19) =3187170a(20) =6659438a(21) =15815050a(22) =27669542a(23) =98100426a(24) =166371218a(25) =437756198a(26) =972187194a(27) =2528368182a(28) =4258122302a(29) =14644463794