**a(1) = 1; for n>1 a(n) is smallest prime not occurring earlier such that the concatenation of a(n), a(n+1), ..., a(2n-1) is a composite number.**

*1, 2, 5, 3, 7, 11, 13, 17, 23, 19, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83*

*2 seqfan posts*

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

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