Sum of every 4th entry of row n in Pascal's triangle, starting at "n choose 0".

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =6a(6) =16a(7) =36a(8) =72a(9) =136a(10) =256a(11) =496a(12) =992a(13) =2016a(14) =4096a(15) =8256a(16) =16512a(17) =32896a(18) =65536a(19) =130816a(20) =261632a(21) =523776a(22) =1048576a(23) =2098176a(24) =4196352a(25) =8390656a(26) =16777216a(27) =33550336a(28) =67100672a(29) =134209536