The Middle C note on a 49-key / 61-key / 76-key piano keyboards

The middle C note on a 49-key piano keyboard:

49-key_piano

The middle C note on a 61-key piano keyboard:

61-key_piano

The middle C not on a 76-key piano keyboard:

76-key_piano

The middle C note on a 88-key piano keyboard:

88-key_piano