Basis for code in A075926.

Terms

a(0) =7a(1) =25a(2) =42a(3) =75a(4) =385a(5) =642a(6) =1155a(7) =2184a(8) =4233a(9) =8330a(10) =16523a(11) =98305a(12) =163842a(13) =294915a(14) =557064a(15) =1081353a(16) =2129930a(17) =4227083a(18) =8421504a(19) =16810113a(20) =33587330a(21) =67141763a(22) =134250632a(23) =268468361a(24) =536903818a(25) =1073774731a(26) =6442450945a(27) =10737418242