a = 1 + 5 + 9 + 13 + ... + 97
nr termeni= (97-1):4 +1=24+1=25 termeni are sirul
a=25x(97+1):2=25x98:2=25x49
a= 5²x 7²=(5x7)²=35² varianta A
suma lui Gauss
aflam pasul 5-1=4
aflam nr termeni= (ultimul termen -primul termen) : pas +1= n
aflam sumS= n x (ultimul termen + primul termen) : 2
