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dati factor comun si apoi calculati:7+14+21+...+147

Răspuns :

7+14+21+...+147=7*(1+2+...+21)=4*21*22:2=924
7+14+21+....+147=7*(1+2+3+...21)=7*(21*22/2)=7*(462/2)=7*231=1617