Explicație pas cu pas:
2+3+4....38=
2+3+4+5+6+7+8+9+10=54
11+12+13+14+15+16+17+18+19+20=155
21+22+23+24+25+26+27+28+29+30=255
31+32+33+34+35+36+37+38=276
54+155+255+276=740