0,1

a(4)= 56 because there are 56 pentagonal numbers with 4 digits.

Cf. A000326.

Sequence in context: A006081 A099511 A143093 this_sequence A106158 A003323 A073591

Adjacent sequences: A117709 A117710 A117711 this_sequence A117713 A117714 A117715

base,nonn

Luc Stevens (lms022(AT)yahoo.com), Apr 13 2006