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 A282509 #22 Feb 27 2017 02:31:23
%S A282509 2,11,17,23,37,491,47,73,79,6043,67,193,197,211,223,5639,211,4783,401,
%T A282509 3467,439,41357,577,617,461,18133,379,60899,157,17827,761,3847,1087,
%U A282509 38201,853,45641,743,59723,113,246173,1249,14831,1847,49177,1741,109141,2011,104053,2399,128599,2281,157127,2917,11149,3023,43913,2539
%N A282509 a(n) is the largest number such that every subsequence of digits of the number written in base n is prime.
%C A282509 For odd n the number will have the form p2, 2p, or p, where p is a prime digit in base n.
%C A282509 For even n the number of digits cannot exceed pi(n)-omega(n)+1 = A048865(n)+1, where pi(n) is the number of primes <= n (A000720), omega(n) is number of distinct primes dividing n (A001221).
%H A282509 Dmitrii Ubskii, <a href="/A282509/b282509.txt">Table of n, a(n) for n = 3..500</a>
%e A282509 In base-12 35B7 (6043 in base-10) is prime, and all of 35B, 357, 3B7, 5B7, 35, 3B, 37, 5B, 57, B7, 3, 5, B, and 7 are prime.
%t A282509 a[b_] := Block[{m,p,r}, p = Select[Range[b-1], PrimeQ]; m = 0; r[n_] := Block[{}, m = Max[m, n]; r /@ Select[n*b+p, PrimeQ[#] && And @@ PrimeQ /@ (FromDigits[#, b] & /@ Subsets[IntegerDigits[#, b], {2, Infinity}]) &];]; r@0; m]; a /@ Range[3, 100] (* _Giovanni Resta_, Feb 21 2017 *)
%Y A282509 Cf. A000720, A001221, A048865.
%K A282509 nonn,base
%O A282509 3,1
%A A282509 _Dmitrii Ubskii_, Feb 17 2017