设自然数个数为n,被擦掉的为a,可知1≤a≤n知可列不定方程n(n+1)/2-a=(16+4/5)(n-1)可知,n(n+1)/2-1≥n(n+1)/2-a=(16+4/5)(n-1)n(n+1)/2-n≤n(n+1)/2-a=(16+4/5)(n-1)解之得,n+2≥(32+8/5)n≤(32+8/5)故有,n只能取32...