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 A135238 #11 Aug 09 2019 06:23:36
%S A135238 1,2,8,2991,65034,880374,2346534651,46464826662,234065340651
%N A135238 Numbers n such that phi(sigma(n)) = reversal(n).
%C A135238 If both numbers 10^m-3 & 5*10^(m-1)-1 are primes and n=3*(10^m-3) then phi(sigma(n))=reversal(n), namely n is in the sequence (the proof is easy). Conjecture: n=2991 is the only such term of the sequence. there is no further term up to 35*10^7.
%C A135238 There are no other terms up to 10^10. - _Donovan Johnson_, Oct 24 2013
%C A135238 If p and 2*p-1 are primes, where p = 3900000*100^t + 108900*10^t + 109, then 6*p-3 is in the sequence. This happens at least for t=1 (2346534651), t=2 (234065340651), t=11, and t=76. - _Giovanni Resta_, Aug 09 2019
%e A135238 phi(sigma(880374)) = phi(1920960) = 473088 = reversal(880374), so 880374 is in the sequence.
%t A135238 reversal[n_]:=FromDigits[Reverse[IntegerDigits[n]]]; Do[If[EulerPhi[DivisorSigma[1,n]]==reversal[n],Print[n]], {n,350000000}]
%o A135238 (PARI) isok(n) = eulerphi(sigma(n)) == fromdigits(Vecrev(digits(n))); \\ _Michel Marcus_, Aug 09 2019
%Y A135238 Cf. A071525, A000010, A000203.
%K A135238 nonn,base,more
%O A135238 1,2
%A A135238 _Farideh Firoozbakht_, Dec 26 2007
%E A135238 a(7) from _Donovan Johnson_, Oct 24 2013
%E A135238 a(8)-a(9) from _Giovanni Resta_, Aug 09 2019