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A075243
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Composite numbers requiring increasingly larger bases to become prime by base reversal.
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1
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4, 6, 8, 9, 16, 27, 36, 78, 81, 102, 114, 144, 270, 420, 480, 750, 1848, 2382, 2940, 13860, 14490, 14520, 21840, 31860, 33660, 44580, 80850, 1228080, 4305210, 5326860, 6846840
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| The bases at which these entries occur are in A074901. See A075242.
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MATHEMATICA
| NextComposite[n_] := Block[{k = n + 1}, While[PrimeQ[k], k++ ]; k]; f[n_] := Block[{b = 2}, While[b < n && !PrimeQ[ FromDigits[ Reverse[ IntegerDigits[n, b]], b]], b++ ]; b]; If[b != n, b, 0]]; b = -1; k = 4; Do[ While[c = f[k]; c <= b, k = NextComposite[k]]; b = c; Print[k], {n, 1, 31}]
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CROSSREFS
| Sequence in context: A095404 A073540 A123710 * A024370 A121719 A162738
Adjacent sequences: A075240 A075241 A075242 * A075244 A075245 A075246
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KEYWORD
| base,hard,nonn
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AUTHOR
| Robert G. Wilson v (rgwv(AT)rgwv.com), Sep 09 2002
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