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 A136543 #6 Nov 03 2012 16:48:03
%S A136543 793,79993,2152311,79999993,7999999993,799999999993
%N A136543 Numbers n such that phi(n)+sigma(n)=4*reversal(n).
%C A136543 All semiprimes of the form 8*10^m-7 are in the sequence - the proof is easy. Next term is greater than 10^8.
%C A136543 a(7) > 10^12. - _Giovanni Resta_, Nov 03 2012
%C A136543 A100412(n) is in the sequence for n = 2, 4, 7, 9, 11, 16, 18, 23, 31, 32, 40,... - _M. F. Hasler_, Nov 03 2012
%e A136543 phi(2152311)+sigma(2152311)=1217664+3312384=4*1132512=4*reversal(2152311), so 2152311 is in the sequence.
%t A136543 Do[If[4*FromDigits@Reverse@IntegerDigits@n==EulerPhi@n+ DivisorSigma[1,n],Print[n]],{n,100000000}]
%K A136543 base,more,nonn
%O A136543 1,1
%A A136543 _Farideh Firoozbakht_, Jan 20 2008
%E A136543 a(5)-a(6) from _Giovanni Resta_, Nov 03 2012