求1000以内奇数，偶数之和

奇数：echo seq 1 1000|sed -n '1~2p'|tr "\n" "+"|sed -r "s/(.*).$/\1/"|bc
seq -s + 1 2 1000 | bc
偶数：echo seq 1 1000|sed -n '2~2p'|tr "\n" "+"|sed -r "s/(.*).$/\1/"|bc
seq -s + 2 2 1000 | bc