👤

19. Calculaţi:
a) 1 + 4 + 7 + 10 + ... + 100;
b) 2 + 8 + 14 +20 + ... +98;
c) 1918 + 1919 + 1920 + 1921 + ... + 2018;
d) 111 + 113 + 115 + 117 + ... + 2017.​