1,1
a(4) is M21, the 21st Mersenne prime with prime digit count of 2917
Cf. A028335.
Sequence in context: A072877 A201378 A032329 * A061490 A048827 A032077
Adjacent sequences: A066224 A066225 A066226 * A066228 A066229 A066230
nonn,base
Enoch Haga (Enokh(AT)comcast.net), Dec 18 2001