rezolvare
1=5·0+1
6=5·1+1
11=5·2+1
16=5·3+1
21=5·4+1
..................
4021=5·804+1
a) (5-0)+1=6
................
(804-0)+1=805
are 805 termeni
b)
S=5·(0+1+2+3+4+....+804)+1·805
I----------S₈₀₄---------I
Sn=n(n+1):2
S₈₀₄=804(804+1):2=804·805:2=323.610
S=5·323.610+1·805=1.618.050+805=1.618.855