Yes, LONGANS is a Scrabble word!

Letter values in Scrabble US: L 1, O 1, N 1, G 2, A 1, N 1, S 1.

Is it a valid word?

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

tree of southeastern Asia to Australia grown primarily for its sweet edible fruit resembling litchi nuts; sometimes placed in genera Euphorbia or Nephelium

Also: dimocarpus longan, euphorbia litchi, nephelium longana.

Not playable in Scrabble US: LUNGEN, LONGANBERRY.