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%I #12 Nov 14 2018 09:34:30
%S 500,15500500,1510001505011550050050015500500
%N a(1) = 500, then a(n) is the concatenation of the roman numerals (I, V, X, L, C, D, M) visible in a(n-1) written in English.
%e a(1) = 500, which is fIVe hunDreD, so a(2) = concat(1, 5, 500, 500) = 15500500, which is fIVeteen MILLIon fIVe hunDreD thousanD fIVe hunDreD, so a(3) = concat(1, 5, 1000, 1, 50, 50, 1, 1, 5, 500, 500, 500, 1, 5, 500, 500), etc.
%Y Cf. A002904, A092302.
%K nonn,word,less
%O 1,1
%A _Pierre CAMI_, Aug 21 2004