A Chebyshev transform of (1+3x)/(1-3x).

Terms

a(0) =1a(1) =6a(2) =17a(3) =42a(4) =109a(5) =288a(6) =755a(7) =1974a(8) =5167a(9) =13530a(10) =35423a(11) =92736a(12) =242785a(13) =635622a(14) =1664081a(15) =4356618a(16) =11405773a(17) =29860704a(18) =78176339a(19) =204668310a(20) =535828591a(21) =1402817466a(22) =3672623807a(23) =9615053952a(24) =25172538049a(25) =65902560198a(26) =172535142545