Variations is, as everyone her undoubtedly knows (so I'm really posting this for the lurkers) based on Paganini's Caprice No. 24 in A minor.
It's a tune that has had considerable mileage. While I haven't heard all of them, the list of variations includes:
Variations on a Theme of Paganini - Boris Blacher.
Paganini Variations, Op. 35, for solo piano - Johannes Brahms
Grandes Etudes de Paganini, S.141, for solo piano - Franz Liszt (one of the five caprices arranged is the 24th)
Paganini Variations - Witold Lutoslawski
Rhapsody on a Theme of Paganini, Op. 43 - Sergei Rachmaninoff
And, of course, Andrew Lloyd, as I earlier stated, put it on his Webber and grilled it.