**a(1) = 3. For n > 1, a(n) is the least unused number such that the concatenation a(n)a(n-1)...a(2)a(1) is prime.**

*3, 1, 6, 9, 4, 20, 13, 29, 19, 2, 7, 18, 12, 41, 36, 30, 72, 25, 27, 8, 28, 42, 47, 114, 85*

*3 seqfan posts*

Index of A-numbers in seqfan: by ascending order by month by frequency by keyword

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