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A088648
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a(1) = 1, then the smallest odd number not occurring earlier such that the concatenation a(r), a(s) is composite for all s > r.
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0
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1, 5, 11, 15, 19, 25, 35, 45, 55, 65, 75, 85, 95, 105, 115, 125, 135, 145, 155, 165, 175, 185, 195, 205, 215, 225, 235, 245, 255, 265, 275, 285, 295, 305, 315, 325, 335, 345, 355, 365, 375, 385, 395, 405, 415, 425, 435, 445, 455, 465, 475, 485, 495, 505, 515
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OFFSET
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0,2
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COMMENTS
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The sequence is infinite with trivial terms of the form 10k+5. Subsidiary sequence: sequence of nontrivial terms. Conjecture: the subsidiary sequence is infinite.
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LINKS
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EXAMPLE
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a(5) = 19 as 119, 519,1119,1519, etc. are all composite.
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CROSSREFS
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KEYWORD
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base,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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