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EXAMPLE
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a(3) = 1: 1|2|3|4|5|6.
a(4) = 34: 12|3|4|5|6|78, 13|2|4|5|6|78, 1|23|4|5|67|8, 1|23|4|5|68|7, 14|2|3|5|6|78, 1|24|3|5|67|8, 1|24|3|5|68|7, 1|2|34|56|7|8, 1|2|34|57|6|8, 1|2|34|58|6|7, 15|2|3|4|6|78, 1|25|3|4|67|8, 1|25|3|4|68|7, 1|2|35|46|7|8, 1|2|35|47|6|8, 1|2|35|48|6|7, 1|2|36|45|7|8, 1|2|37|45|6|8, 1|2|38|45|6|7, 16|2|3|4|5|78, 1|26|3|4|57|8, 1|26|3|4|58|7, 1|2|36|47|5|8, 1|2|36|48|5|7, 1|2|37|46|5|8, 1|2|38|46|5|7, 1|27|3|4|56|8, 1|28|3|4|56|7, 17|2|3|4|5|68, 1|27|3|4|58|6, 1|2|37|48|5|6, 1|2|38|47|5|6, 1|28|3|4|57|6, 18|2|3|4|5|67.
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