Perry's Index to the Aesopica
Perry reserves 421 for a long joke between a son and his father about
counting eggs. Perry found the joke in a Byzantine manuscript, cod. Atheniensis
You can find a compilation of Perry's index to the Aesopica in the gigantic appendix to his
edition of Babrius and Phaedrus for the Loeb Classical Library
(Harvard University Press: Cambridge, 1965). This book is an absolute must for anyone interested
in the Aesopic fable tradition. Invaluable.