Further to my reply to sibling-reply finnw, here's the pattern of digits, further showing his 10 * 9, etc., breakdown. $ pins | > sed -r ' > :a

Further to my reply to sibling-reply finnw, here's the pattern of digits, further showing his 10 * 9, etc., breakdown. $ pins | > sed -r ' > :a; s/^([0-9])(.*)\1/\1\2a/; ta; s/[0-9]/a/ > :b; s/a([0-9])(.*)\1/a\1\2b/; tb; s/[0-9]/b/ > s/([0-9])\1/cc/; s/[0-9]/c/ > s/[0-9]/d/ > ' | > sort | uniq -c | sort -n 10 aaaa 90 aaab 90 aaba 90 aabb 90 abaa 90 abab 90 abba 90 abbb 720 aabc 720 abac 720 abbc 720 abca 720 abcb 720 abcc 5040 abcd $