Shifts left when Dirichlet convolution with a (DC:(b,a)->c) applied twice.

Terms

a(0) =1a(1) =1a(2) =3a(3) =9a(4) =30a(5) =90a(6) =288a(7) =864a(8) =2647a(9) =7968a(10) =24084a(11) =72252a(12) =217467a(13) =652401a(14) =1958931a(15) =5877333a(16) =17637453a(17) =52912359a(18) =158754606a(19) =476263818a(20) =1428840972a(21) =4286528100a(22) =12859728804a(23) =38579186412a(24) =115738013592a(25) =347214043476