This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A075243 #9 Jun 04 2021 03:16:59
%S A075243 4,6,8,9,16,27,36,78,81,102,114,144,270,420,480,750,1848,2382,2940,
%T A075243 13860,14490,14520,21840,31860,33660,44580,80850,1228080,4305210,
%U A075243 5326860,6846840,9796710,9990750,10720710,14910630,15129510,15278250,16785090,17022390,17608500
%N A075243 Composite numbers requiring increasingly larger bases to become prime by base reversal.
%C A075243 The bases at which these entries occur are in A074901. See A075242.
%H A075243 Amiram Eldar, <a href="/A075243/b075243.txt">Table of n, a(n) for n = 1..48</a>
%t A075243 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 A075243 Cf. A074901, A075242.
%K A075243 base,hard,nonn
%O A075243 1,1
%A A075243 _Robert G. Wilson v_, Sep 09 2002
%E A075243 More terms from _Amiram Eldar_, Jun 04 2021