Yes, CALCULI is a Scrabble word!

Letter values in Scrabble US: C 3, A 1, L 1, C 3, U 1, L 1, I 1.

Is it a valid word?

CALCULI is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a hard lump produced by the concretion of mineral salts; found in hollow organs or ducts of the body
an incrustation that forms on the teeth and gums
the branch of mathematics that is concerned with limits and with the differentiation and integration of functions

Also: infinitesimal calculus.