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A242377
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Greatest n-digit prime in which every two-digit string is also a prime.
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3
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7, 97, 971, 9719, 97973, 979717, 9797371, 97973731, 979797979, 9797979713, 97979797171, 979797973117, 9797979797971, 97979797973173, 979797979797317, 9797979797979719, 97979797979797373, 979797979797971179, 9797979797979737971
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OFFSET
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1,1
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COMMENTS
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To stay parallel with A090534, a(1) exists.
The greatest potential candidate, gpc(n), is of the form floor(10^n*97/99). The following is gpc(n)-a(n): 2, 0, 8, 78, 6, 80, 608, 6066, 0, 84, 808, 6680, 8, 6624, 662, 78, 606, 8618, 60008, 86, 600, 6000, 660, 608060, 808, ... .
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LINKS
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MATHEMATICA
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fQ[p_] := Block[{id = IntegerDigits@ p}, Union@ PrimeQ[ FromDigits@# & /@ Partition[id, 2, 1]] == {True}]; f[n_] := Block[{p = NextPrime[10^n*97/99, -1]}, While[ !fQ@ p, p = NextPrime[p, -1]]; p]; f[1] = 7; Array[f, 19]
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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