a(n) = T(4,n), array T given by A048483.

Terms

a(0) =1a(1) =6a(2) =16a(3) =36a(4) =76a(5) =156a(6) =316a(7) =636a(8) =1276a(9) =2556a(10) =5116a(11) =10236a(12) =20476a(13) =40956a(14) =81916a(15) =163836a(16) =327676a(17) =655356a(18) =1310716a(19) =2621436a(20) =5242876a(21) =10485756a(22) =20971516a(23) =41943036a(24) =83886076a(25) =167772156a(26) =335544316a(27) =671088636a(28) =1342177276a(29) =2684354556