NutriSystem — the Horsham, Pa.-based online weight-loss company — has bulked up. Its first-quarter 2006 revenues grew 292%, to $146.8 million, and net income rose 592%, with analysts predicting continued sharp increases in 2006. Memories of its bankruptcy filing and litigation woes under previous owners have all but been erased, even as the company plans to target new customer segments and expand internationally. And yet, according to its two top executives, there has been as much luck and grit as glamour and glitz in the company’s rise from the ashes. “Sometimes you learn more from your mistakes than from your successes,” said president and COO George Jankovic, 38, who came to this country in 1991 from Serbia to study electrical engineering at the University of Colorado. “It’s not like everything we found was gold.…