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 A099079 #27 Feb 16 2025 08:32:54
%S A099079 2,3,9,28,30,31,51,127,208
%N A099079 Numbers n such that phi(n).phi(n-1). ... .phi(2).phi(1) is prime (dots between numbers mean concatenation).
%C A099079 Number of digits of primes corresponding to the nine known terms of this sequence are respectively 2,3,9,39,42,44,84,244,441.
%C A099079 If it exists, a(10) > 10362. - _J.W.L. (Jan) Eerland_, Aug 14 2022
%C A099079 If it exists, a(10) > 25000. - _Michael S. Branicky_, Aug 23 2024
%H A099079 Carlos Rivera, <a href="http://www.primepuzzles.net/puzzles/puzz_008.htm">Puzzle 8. Primes by Listing</a>, The Prime Puzzles & Problems connection.
%H A099079 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/IntegerSequencePrimes.html">Integer Sequence Primes</a>
%e A099079 9 is in the sequence because phi(9).phi(8).phi(7).phi(6).phi(5).phi(4).phi(3).phi(2).phi(1) = 646242211 is prime.
%t A099079 Module[{nn=210,eph},eph=EulerPhi[Range[nn]];Position[Table[FromDigits[ Flatten[ IntegerDigits[Reverse[Take[eph,n]]]]],{n,nn}],_?PrimeQ]]// Flatten (* _Harvey P. Dale_, Apr 21 2020 *)
%t A099079 ParallelTable[If[PrimeQ[ToExpression[StringJoin[ToString[#]&/@Reverse[Table[EulerPhi[k],{k,1,n}]]]]],n,Nothing],{n,1,10^4}]//.{}->Nothing (* _J.W.L. (Jan) Eerland_, Aug 15 2022 *)
%Y A099079 Cf. A046035, A099077, A099078, A099080.
%K A099079 base,more,nonn
%O A099079 1,1
%A A099079 _Farideh Firoozbakht_, Oct 23 2004