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 A020994 #28 Jul 16 2022 11:48:42
%S A020994 2,3,5,7,23,37,53,73,313,317,373,797,3137,3797,739397
%N A020994 Primes that are both left-truncatable and right-truncatable.
%C A020994 Two-sided primes: deleting any number of digits at left or at right, but not both, leaves a prime.
%C A020994 Primes in which every digit string containing the most significant digit or the least significant digit is prime. - _Amarnath Murthy_, Sep 24 2003
%C A020994 Intersection of A024785 and A024770. - _Robert Israel_, Mar 23 2015
%D A020994 David Wells, The Penguin Dictionary of Curious and Interesting Numbers, p. 178 (Rev. ed. 1997).
%H A020994 I. O. Angell and H. J. Godwin, <a href="http://dx.doi.org/10.1090/S0025-5718-1977-0427213-2">On Truncatable Primes</a> Math. Comput. 31, 265-267, 1977.
%H A020994 Patrick De Geest, <a href="http://www.worldofnumbers.com/truncat.htm">The list of 4260 left-truncatable primes</a>
%H A020994 <a href="/index/Tri#tprime">Index entries for sequences related to truncatable primes</a>
%t A020994 tspQ[n_] := Module[{idn=IntegerDigits[n], l}, l=Length[idn]; Union[PrimeQ/@(FromDigits/@ Join[Table[Take[idn, i], {i, l}], Table[Take[idn, -i], {i, l}]])]=={True}] Select[Prime[Range[PrimePi[740000]]], tspQ]
%Y A020994 Cf. A033664, A024785, A032437, A024770, A052023, A052024, A052025, A050986, A050987, A254751, A254753.
%K A020994 nonn,fini,full,base
%O A020994 1,1
%A A020994 Mario Velucchi (mathchess(AT)velucchi.it)
%E A020994 Corrected by _David W. Wilson_
%E A020994 Additional comments from _Harvey P. Dale_, Jul 10 2002