This sounds like it should be a fairly straightforward question to answer but I haven't found it yet, only figures of main + universe, which is various figures over 24,000 depending on release.
You can run the following command line:
for f in /var/lib/apt/lists/*Packages; do
printf '%5d %s
' $(grep '^Package: ' "$f" | wc -l) ${f##*/}
done | sort -n
that on my machine show the following output
27433 it.archive.ubuntu.com_ubuntu_dists_oneiric_universe_binary-i386_Packages
7768 it.archive.ubuntu.com_ubuntu_dists_oneiric_main_binary-i386_Packages
1944 it.archive.ubuntu.com_ubuntu_dists_oneiric-updates_main_binary-i386_Packages
664 it.archive.ubuntu.com_ubuntu_dists_oneiric_multiverse_binary-i386_Packages
632 security.ubuntu.com_ubuntu_dists_oneiric-security_main_binary-i386_Packages
605 it.archive.ubuntu.com_ubuntu_dists_oneiric-updates_universe_binary-i386_Packages
167 security.ubuntu.com_ubuntu_dists_oneiric-security_universe_binary-i386_Packages
67 it.archive.ubuntu.com_ubuntu_dists_oneiric-backports_universe_binary-i386_Packages
24 it.archive.ubuntu.com_ubuntu_dists_oneiric-updates_multiverse_binary-i386_Packages
21 it.archive.ubuntu.com_ubuntu_dists_oneiric_restricted_binary-i386_Packages
13 extras.ubuntu.com_ubuntu_dists_oneiric_main_binary-i386_Packages
12 archive.canonical.com_ubuntu_dists_oneiric_partner_binary-i386_Packages
11 it.archive.ubuntu.com_ubuntu_dists_oneiric-backports_main_binary-i386_Packages
10 security.ubuntu.com_ubuntu_dists_oneiric-security_multiverse_binary-i386_Packages
6 it.archive.ubuntu.com_ubuntu_dists_oneiric-updates_restricted_binary-i386_Packages
0 security.ubuntu.com_ubuntu_dists_oneiric-security_restricted_binary-i386_Packages
0 it.archive.ubuntu.com_ubuntu_dists_oneiric-backports_restricted_binary-i386_Packages
0 it.archive.ubuntu.com_ubuntu_dists_oneiric-backports_multiverse_binary-i386_Packages
