a(n) = A069537(n)/2.

Terms

a(0) =1a(1) =10a(2) =55a(3) =100a(4) =505a(5) =550a(6) =1000a(7) =5005a(8) =5050a(9) =5500a(10) =10000a(11) =50005a(12) =50050a(13) =50500a(14) =55000a(15) =100000a(16) =500005a(17) =500050a(18) =500500a(19) =505000a(20) =550000a(21) =1000000a(22) =5000005a(23) =5000050a(24) =5000500a(25) =5005000a(26) =5050000a(27) =5500000a(28) =10000000a(29) =50000005