1,1

Written in Roman numerals this sequence begins II, V, XI, LIX, CI, DIX, MIX, MLI, MMMI.

For a while I actually considered putting in 97 (XCVII) instead of 101 (CI), since XCVII contains CI as a substring. But it also contains II, V and XI as substrings, so going in order strictly from smallest to greatest, 97 must be excluded.

a(4) = 59 because it is a prime number and in Roman numerals it's written LIX (all the substrings are composite or not prime: L, LI, LX, I, IX, X).

Cf. A071062, minimal set of prime-strings in base 10.

Adjacent sequences: A131477 A131478 A131479 this_sequence A131481 A131482 A131483

Sequence in context: A089609 A087185 A127010 this_sequence A018847 A134996 A134998

base,nonn

Robert Happelberg (roberthappelberg(AT)yahoo.com), Jul 27 2007