cp's OEIS Frontend

A251808 Numbers n such that if m = reverse(phi(n)) then n = reverse(phi(m)).

%I A251808 #9 Jan 16 2015 10:07:10
%S A251808 1,21,63,291,2744,2991,6102,6711,46676013,69460293,272543398,896172631
%N A251808 Numbers n such that if m = reverse(phi(n)) then n = reverse(phi(m)).
%C A251808 Fixed points of the transform n -> reverse(phi(reverse(phi(n)))).
%C A251808 A072395 is a subset of this sequence.
%C A251808 No further terms up to 10^9. - _Felix Fröhlich_, Dec 30 2014
%e A251808 phi(2744) = 1176 and reverse(1176) = 6711;
%e A251808 phi(6711) = 4472 and reverse(4472) = 2744;
%p A251808 with(numtheory):T:=proc(w) local x,y,z; x:=0; y:=w;
%p A251808 for z from 1 to ilog10(w)+1 do x:=10*x+(y mod 10); y:=trunc(y/10); od; x; end:
%p A251808 P:=proc(q) local k,n; for n from 1 to q do if n=T(phi(T(phi(n))))
%p A251808 then print(n); fi; od; end: P(10^12);
%o A251808 (PARI) for(n=1, 1e9, m=eval(concat(Vecrev(Str(eulerphi(n))))); if(n==eval(concat(Vecrev(Str(eulerphi(m))))), print1(n, ", "))) \\ _Felix Fröhlich_, Dec 30 2014
%Y A251808 Cf. A000010, A072395.
%K A251808 nonn,base,more
%O A251808 1,2
%A A251808 _Paolo P. Lava_, Dec 09 2014
%E A251808 a(9)-a(12) from _Felix Fröhlich_, Dec 30 2014