Question

1+3+5+...+2011
2005+2+4+6+...+4008
42+43+44+...+347
121+122+123+...+854
1+4+7+10+...+541
1+5+9+13+...+725
22+25+28+...+301
32+39+46+...+753
4+8+12+16+...+2012
7+14+21+28+...+2016

Answer 1

1+3+5+...+2011=(2011x2012):2-2x(1006x1007):2=2011x1006-1006x1007=1006x1004=1010024


2005+2+4+...+4008=2005+2(1+2+3+...+2004)=4020025


42+43+44+...+347=347x174-41x21=59517

121+122+...+854=855x427-60x121=357825

1+4+7+...+541=272x542=147424


1+5+9+...+725=363x726=269558

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