'गणित सार संग्रह' किस प्राचीन भारतीय गणितज्ञ द्वारा रचित एक प्रसिद्ध ऐतिहासिक कृति है?

What is the ratio of the perimeter to the diameter of a circle according to Aryabhata?

Which Indian mathematician made significant contributions to the theory of numbers, fractional differentiation, and mock theta functions in the early 20th century?