This number is a prime.
Just showing those entries submitted by 'Green': (Click here to show all)
The digits of the prime 15559 appear as the final digits of the numbers in the sequence of centered tetrahedral numbers. The pattern 1-5-5-5-9 repeats for each successive group of 5 consecutive numbers in the sequence. The first five numbers in the sequence are 1,5,15,35,69. (15559 is also the zip code of Schellsburg PA.) [Green]