1+5+9+13+17+21...+1001=?

1+5+9+13+17+21...+1001 =1+(1+4)+(1+4*2)+(1+4*3)+(1+4*4)+(1+4*5).+(1+4*250) =251+4(1+2+3+4+5...+250) =251+4*(1+250)*250/2 =125751