Definition :

ð(1...q)[F(k) ] = multiplications of F(k) from k=1 to k=q .

F(k)=(a^2+a*n*d-a*d-n*d^2)+[(n+1)*d^2*k-d^2*k^2]

for even n the solution is :

ð(1...n/2)[F(k)]

for odd n, the solution is :

(a+0.5*d*(n-1) )*ð (1...(n-1)/2 )F(k)

blackjack

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