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A075243
Composite numbers requiring increasingly larger bases to become prime by base reversal.
2
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, 9796710, 9990750, 10720710, 14910630, 15129510, 15278250, 16785090, 17022390, 17608500
OFFSET
1,1
COMMENTS
The bases at which these entries occur are in A074901. See A075242.
LINKS
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}]
CROSSREFS
Sequence in context: A095404 A073540 A123710 * A024370 A367176 A121719
KEYWORD
base,hard,nonn
AUTHOR
Robert G. Wilson v, Sep 09 2002
EXTENSIONS
More terms from Amiram Eldar, Jun 04 2021
STATUS
approved