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 A185222 #19 Oct 18 2019 11:25:47
%S A185222 6,42,1806,2786,47058,73178,85082,2143066830,2214502422,3138798830,
%T A185222 4404051298,4428107218,4428595298
%N A185222 Composite numbers n such that (n'+1)' = n', where n' is the arithmetic derivative of n.
%C A185222 All primes are a solution to this equation. For composite numbers, a(8) > 10^7.
%C A185222 No more terms below 4.8*10^10. - _Amiram Eldar_, Oct 18 2019
%t A185222 dn[0]=0; dn[1]=0; dn[n_] := Module[{f=Transpose[FactorInteger[n]]}, If[PrimeQ[n], 1, Plus@@(n*f[[2]]/f[[1]])]]; Select[Range[2,100000], !PrimeQ[#] && dn[#] == dn[dn[#]+1]&]
%Y A185222 Cf. A003415, A203618 (solutions of the differential equation (n'-1)' = n-1).
%K A185222 nonn,more
%O A185222 1,1
%A A185222 _José María Grau Ribas_, Jan 24 2012
%E A185222 a(8)-a(13) from _Amiram Eldar_, Oct 18 2019