a(4) has 292 digits and is too large to include.
Table of n, a(n) for n=1..3.
Cf. A000215, A053067, A133013.
Sequence in context: A160362 A155852 A003392 * A100339 A195626 A332153
Adjacent sequences: A133023 A133024 A133025 * A133027 A133028 A133029
Omar E. Pol, Nov 09 2007