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 A240768 #11 Feb 16 2025 08:33:21 %S A240768 2,5,773,3373,3947,4643,5113,6397,6967,7937,15647,16823,24373,33547, %T A240768 34337,37643,56983,57853,59743,62383,63347,63617,69337,72467,72617, %U A240768 75653,76367,87643,92683,97883,98317,121997,124337,163853,213613,236653,242467,242797 %N A240768 Left-truncatable primes p with property that prepending any single decimal digit to p does not produce a prime. %H A240768 Chris Caldwell, The Prime Glossary, <a href="https://t5k.org/glossary/xpage/LeftTruncatablePrime.html">Left-truncatable prime</a> %H A240768 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TruncatablePrime.html">Truncatable Prime</a> %H A240768 <a href="/index/Tri#tprime">Index entries for sequences related to truncatable primes</a> %F A240768 A024785 INTERSECT A155762. %e A240768 3373 belongs to this sequence because 3373, 373, 73 and 3 are all prime; k*10^4 + 3373, for k = 1 to 9, are all composite. %o A240768 (PARI) for(n=2, 242797, v=n; while(isprime(n), c=n; n=lift(Mod(c, 10^(#Str(c)-1))); if(!(#Str(c)-#Str(n)==1), break)); if(n==0, s=#Str(v); t=0; for(k=1, 9, if(isprime(k*10^s+v), break, t++)); if(t==9, print1(v, ", "))); n=v); %Y A240768 Subsequence of A024785 and of A155762. %K A240768 nonn,base,fini %O A240768 1,1 %A A240768 _Arkadiusz Wesolowski_, Apr 12 2014