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a1=1
r=6
sn=2a1 + (n-1)r *n /2
(2+6n-6 )*n=560
(6n-4)n=560
6n^2 -4n-560=0
pierw z delty= 116
n1=4+116/12
n=10
10 to liczba wyrazow w sumie ciagów
1 + 7 +13 +19+ 25+31+37+43+49+55=280