Length of Roman notation for n = length of decimal representation.

Terms

a(0) =1a(1) =5a(2) =11a(3) =15a(4) =20a(5) =40a(6) =51a(7) =55a(8) =60a(9) =90a(10) =102a(11) =104a(12) =106a(13) =109a(14) =111a(15) =115a(16) =120a(17) =140a(18) =151a(19) =155a(20) =160a(21) =190a(22) =201a(23) =205a(24) =210a(25) =250a(26) =300a(27) =401a(28) =405a(29) =410