Numbers of the form (3^{mr}-1)/(3^r-1) for positive integers m, r.

Terms

a(0) =1a(1) =4a(2) =10a(3) =13a(4) =28a(5) =40a(6) =82a(7) =91a(8) =121a(9) =244a(10) =364a(11) =730a(12) =757a(13) =820a(14) =1093a(15) =2188a(16) =3280a(17) =6562a(18) =6643a(19) =7381a(20) =9841a(21) =19684a(22) =20440a(23) =29524a(24) =59050a(25) =59293a(26) =66430a(27) =88573a(28) =177148a(29) =265720