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A075243 Composite numbers requiring increasingly larger bases to become prime by base reversal. 2

%I

%S 4,6,8,9,16,27,36,78,81,102,114,144,270,420,480,750,1848,2382,2940,

%T 13860,14490,14520,21840,31860,33660,44580,80850,1228080,4305210,

%U 5326860,6846840,9796710,9990750,10720710,14910630,15129510,15278250,16785090,17022390,17608500

%N Composite numbers requiring increasingly larger bases to become prime by base reversal.

%C The bases at which these entries occur are in A074901. See A075242.

%H Amiram Eldar, <a href="/A075243/b075243.txt">Table of n, a(n) for n = 1..48</a>

%t 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}]

%Y Cf. A074901, A075242.

%K base,hard,nonn

%O 1,1

%A _Robert G. Wilson v_, Sep 09 2002

%E More terms from _Amiram Eldar_, Jun 04 2021

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Last modified October 23 00:39 EDT 2021. Contains 348211 sequences. (Running on oeis4.)