** Shares of Pegasystems PEGA.O up 6.6% premarket to $104.98, over three-mth high, as software firm set to join S&P MidCap 400 index .IDX this week

** PEGA to replace Nordstrom JWN.N in the IDX effective Thurs, May 22, the S&P Dow Jones Indices announced

** The Nordstrom family and Mexican retailer El Puerto de Liverpool LIVEPOLC1.MX to take Nordstrom private in $4 bln deal

** Pegasystems, which provides software solutions for customer engagement and business process management, posted Q1 adj EPS of $1.53, handily topping analysts' estimate of 49 cents, sending its shares up nearly 29% on Apr 23 to $88.55

** Waltham, Massachusetts-headquartered co has ~85.6 mln shares outstanding for $8.4 bln market cap, per LSEG

** Through Mon close, PEGA up ~6% YTD

** Of 14 analysts covering PEGA, recommendation breakdown is 11 "strong buy" or "buy" and 3 "hold"; median PT of $102 up from $97 a month ago

(Lance Tupper is a Reuters market analyst. The views expressed are his own)

((lance.tupper@tr.com 1-646-279-6380))