set talk off
clea
s=28
dimen a[s]
a[1]=3
a[2]=4
a[3]=5
for n=4 to s
a[n]=a[n-1]+a[n-2]+a[n-3]
endfor
"第28项是",a[s]
set talk on
如果要求任意项,用下边的：
set talk off
input "请输入项数："to s
if s