/home/lee#bash
/home/lee#echo $((1000000*(1000000+1)/2))
500000500000
/home/lee#echo
bash
/home/lee#exit
/home/lee#echo
-ksh
/home/lee#echo $((1000000*(1000000+1)/2))
-363189984 #Error!!!Why?
/home/lee#seq 1 1000000|awk 'END{print sum}'
5e+11