(7⁰ +7¹ +7²+...+7²⁰⁰¹)+1= (1+7+7²+....+7²⁰⁰¹) +1
7²⁰⁰¹= (......7)
S=[(1+7²⁰⁰¹) *2002/2 ]+1
7¹=(.....7)
7²=(......9)
7³=(.......3)
7⁴=(.......1)
7⁵=(........7)
se repeta din 4 in 4
2001:4=500 rest 1 =>7²⁰⁰¹ =(....7)
S= [1+ (......7) *1001] +1
S= (.....8)*1001 +1
S= (........8) +1
S=(.......9) -este pp