Mādhava of Sangamagrāma (~1400) - Gregory - Leibniz Series
4 4 4 4 4
--- - --- + --- - --- + --- ...
1 3 5 7 9
Nilakantha Series
4 4 4 4
3 + --- - --- + --- - --- ...
2*3*4 4*5*6 6*7*8 8*9*10