Letters in the English alphabet.
Black cards in a full deck and,
conversely,
red cards in a full deck.
The atomic number of iron, count of protons and electrons but
not its neutrons.
President Teddy Roosevelt.
Bones in the human foot.
The "Old Enough to Fight, Old Enough to Vote" amendment or,
ironically,
"Prohibition" plus "Protection against Cruel and Unusual Punishment."
Dimensions in bosonic string theory.
An opal wedding anniversary.
The numeric value of the Hebrew name of God in the Bible, which
only appears once.
Asteroid Proserpina.
Ganglions in the sympathetic system.
Ganglions in the sympathetic system.
Rhombicuboctahedron.