Shares of Sandisk surged past $1,800 on September 21, building on a blistering 17%+ run in just four trading sessions, as the memory-chip maker officially joine

Shares of Sandisk surged past $1,800 on September 21, building on a blistering 17%+ run in just four trading sessions, as the memory-chip maker officially joined the S&P 100 index before Monday's open. The inclusion crowns a remarkable stretch for a company that was spun off from Western Digital onl…