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 A237521 #22 Jul 14 2021 10:03:37 %S A237521 2,22605,26026,492775589 %N A237521 Numbers k such that phi(k) + sigma(k) = reversal(k) + 2. %C A237521 a(5), if it exists, is larger than 10^13. %C A237521 Up to 10^13 the equation phi(k) + sigma(k) = reversal(k) - 2 is satisfied only by k = 26330276. %e A237521 22605 is in the sequence because phi(22605) = 10880, sigma(22605) = 39744, and 10880 + 39744 = 50622 + 2, where 50622 is the reversal of 22605. %t A237521 Select[Range[493*10^6],EulerPhi[#]+DivisorSigma[1,#]== IntegerReverse[ #]+2&] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Jan 01 2020 *) %Y A237521 Cf. A000010, A000203, A004086. %Y A237521 Cf. A070272, A230004, A230005, A230006, A230019, A136544, A237522. %K A237521 nonn,base,more %O A237521 1,1 %A A237521 _Giovanni Resta_, Feb 08 2014