Found the following hamletworks.org entries referring to line 21

View Commentary Note for 20
20 Hora. Friends to this ground.1.1.15

View Commentary Note for 21
21 Mar. And Leedgemen to the Dane,1.1.15

View Material Textual Note for 21
21 Mar. And Leedgemen to the Dane,1.1.15

View Commentary Note for 5-6
5-6 Fran. Nay answere me. Stand and vnfolde | your selfe.1.1.2

View Commentary Note for 61
61 In which the Maiestie of buried Denmarke1.1.48

View Commentary Note for 7
7 Bar. Long liue the King,1.1.3

View Material Textual Note for 7
7 Bar. Long liue the King,1.1.3