This is the 4854th most frequent Russian word.
интересны
"Interesting" (plural form).
The word 'интересна' is an adjective in the feminine singular form and is used here as a predicate to describe the book.
Эта книга интересна мне.
This book is interesting to me.
The word 'интересны' is in the plural form since it describes the plural noun 'идеи' (ideas).
Ваши идеи очень интересны.
Your ideas are very interesting.
The word 'интересными' is in the instrumental plural form, agreeing with the plural noun 'фактами' (facts).