6*n analog to Keith numbers.

Terms

a(0) =9a(1) =23a(2) =85a(3) =88a(4) =208a(5) =953a(6) =12339a(7) =122420a(8) =251925a(9) =286400a(10) =467608a(11) =1207360a(12) =1308519a(13) =1537214a(14) =1638373a(15) =1844108a(16) =2314739a(17) =2736742a(18) =9331102a(19) =11692851a(20) =28349534a(21) =85403569