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 A039954 #37 Mar 26 2025 11:30:23
%S A039954 3,313,31415926535897932384626433833462648323979853562951413
%N A039954 Palindromic primes formed from the reflected decimal expansion of Pi.
%C A039954 _Carlos Rivera_ reports that the next two members of this sequence have 301 and 921 digits. The first has been tested with APRTE-CLE. The second one is only a StrongPseudoPrime at the moment. - May 16 2003
%C A039954 Thomas Spahni reports that the fifth member of this sequence with 921 digits is prime. He used Francois Morain's ECPP-V6.4.5a which proved primality in 14913.7 seconds running on a Celeron Core2 CPU at 2.00GHz. - Jun 05 2008
%C A039954 Primes in A135697. Terms with an odd number of digits are the primes in A135698. - _Omar E. Pol_, Mar 06 2012
%H A039954 C. K. Caldwell and G. L. Honaker, Jr., Prime Curios!, <a href="https://t5k.org/curios/page.php?curio_id=725">31414...51413 (53-digits)</a>
%H A039954 Shyam Sunder Gupta, <a href="https://doi.org/10.1007/978-981-97-2465-9_19">Mystery of pi</a>, Exploring the Beauty of Fascinating Numbers, Springer (2025) Ch. 19, 473-497.
%H A039954 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PalindromicPrime.html">Palindromic Prime.</a>
%t A039954 Select[Table[p = Flatten[RealDigits[Pi, 10, d]]; (FromDigits[p] - 1)*10^(Length[p] - 3) + FromDigits[Drop[Reverse[p], 2]], {d, 27}], PrimeQ] (* _Arkadiusz Wesolowski_, Dec 18 2011 *)
%Y A039954 Cf. A002385, A119351, A135697, A135698.
%K A039954 base,nonn,bref
%O A039954 1,1
%A A039954 _G. L. Honaker, Jr._