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140+141+142+...+355+356+357
(SUMA LUI GAUSS)


Răspuns :

357x358:2 -1+2+2+...+139=
357x179-139x140:2=
357x179-139x70=
63903-9730=54173



numarul de termeni este:
n=(357-140)/1 +1=217+1=218
S=(140+357)·218/2=497·109=54173