Mental calculators from history

Aitken, Alexander Craig, [1]
Ampère, André-Marie
Bidder, George Parker
Buxton, Jedediah
Colburn, Zerah
Dase, Johann Zacharias
Deshong, Peter M.
De Grote, Herbert
Devi, Shakuntala
Diamandi, Pericles
Dysart, Willis (a.k.a. Willie the Wizard)
Eberstark, Hans
Euler, Leonhard
Finkelstein, Salo
Fuller, Thomas
Gauss, Carl Friedrich
Griffith, Arthur F.
Hamilton, William Rowan
Inaudi, Jacques
Klein, Wim (a.k.a. Willem Klein) [2]
McCartney, Daniel
Neumann, John von
Ramanujan, Srinivasa
Riemann, Bernhard
Ruckle, Gottfried
Safford, Truman Henry
Shelushkov, Igor
Wallis, Johnnt.