6 + 11 + 16 + 21 + ... + 506 = 25 856
→ stabilesc cati termeni are suma cu ratia = 5 ( 11 - 6= 5; 16 - 11 = 5;..... )
( 506 - 6 ) : 5 + 1 = 500 : 5 + 1 = 101 termeni are suma
→ aplic formula sumei lui Gauss
= 101 × ( 6 + 506 ) : 2 =
= 101 × 512 : 2 =
= 101 × 256 =
= 25 856