text: console.log('Running solution for Problem 0206...');
  console.time('run time');
  
  let searchStart = 1389026623;  // sqrt of 1929394959697989990, pattern with all nines
  let searchStop = 1010101010;  // sqrt of 1020304050607080900, pattern with all zeros
  
  let answer = 0;
  for (var i = searchStart; i >= searchStop; i--) {
    var answerCandStr = (BigInt(i)*BigInt(i)).toString();
    if (answerCandStr.match(/1\d2\d3\d4\d5\d6\d7\d8\d9\d0/gm)) {
      answer = i;
      console.log('>', i);
      console.log('>', BigInt(i)*BigInt(i));
      console.log('> 1_2_3_4_5_6_7_8_9_0');
      break;
    }
  }
  
  console.log('Find the unique positive integer whose square has the form 1_2_3_4_5_6_7_8_9_0.');
  console.log('Answer:', answer);
  
  console.timeLog('run time');
  
  // > 1389019170
  // > 1929374254627488900n
  // > 1_2_3_4_5_6_7_8_9_0
  // Answer: 1389019170
  // run time: 7.124ms
  