70000...00003 (216-digits)

This number is a prime.

                                                                      700000
0000000000 0700000022 2222000000 0000222222 2222000000 0222000002 2220000000
0000002222 0000000000 0002222000 0000000000 2222000000 0000002222 0000000000
0022220000 0000000002 2222222222 2000000222 2222222220 0070000000 0000000003

Just showing those entries submitted by 'Caldwell': (Click here to show all)

700000000000000007
000000222222000000
000022222222220000
000222000002222000
000000000022220000
000000000222200000
000000002222000000
000000222200000000
000022220000000000
000222222222222000
000222222222222000
700000000000000003

This large odd prime becomes small and even when written as a 12-by-18 array with the 2s highlighted. [Caldwell]