Sum of every 4th entry of row n in Pascal's triangle, starting at "n choose 1".

Terms

a(0) =0a(1) =1a(2) =2a(3) =3a(4) =4a(5) =6a(6) =12a(7) =28a(8) =64a(9) =136a(10) =272a(11) =528a(12) =1024a(13) =2016a(14) =4032a(15) =8128a(16) =16384a(17) =32896a(18) =65792a(19) =131328a(20) =262144a(21) =523776a(22) =1047552a(23) =2096128a(24) =4194304a(25) =8390656a(26) =16781312a(27) =33558528a(28) =67108864a(29) =134209536