Sum of every 4th entry of row n in Pascal's triangle, starting at binomial(n,2).

Terms

a(0) =0a(1) =0a(2) =1a(3) =3a(4) =6a(5) =10a(6) =16a(7) =28a(8) =56a(9) =120a(10) =256a(11) =528a(12) =1056a(13) =2080a(14) =4096a(15) =8128a(16) =16256a(17) =32640a(18) =65536a(19) =131328a(20) =262656a(21) =524800a(22) =1048576a(23) =2096128a(24) =4192256a(25) =8386560a(26) =16777216a(27) =33558528a(28) =67117056a(29) =134225920