AKS, Pascal, Primality and Subset-sum

Something in the back of my mind nags about the square of Pascal, primality and subset-sum. I read some of Scott Aaronson lectures which got me to think again on irreversibility, XOR-SAT, linear algorithms, BPP=P and BQP.

Why is testing primality on the nth line of Pascal's square seen as exponential? Looks like cubic, but prohibitive, to me. Missing stuff. Having a look at Karatsuba and Strassen again.

Stopped programming for a while and am looking what gives if you simplify SUBSET-SUM by manipulating out unknowns. Guess I need a hobby.

Quantum dump, while programming.