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

1, 21, 63, 291, 2744, 2991, 6102, 6711, 46676013, 69460293, 272543398, 896172631

Offset: 1

Author

Paolo P. Lava, Dec 09 2014

Keywords

• nonn
• base
• more

Comments

Fixed points of the transform n -> reverse(phi(reverse(phi(n)))).

A072395 is a subset of this sequence.

No further terms up to 10^9. - Felix Fröhlich, Dec 30 2014

Examples

			phi(2744) = 1176 and reverse(1176) = 6711;
phi(6711) = 4472 and reverse(4472) = 2744;
		

Crossrefs

Cf. A000010, A072395.

Programs

Maple

with(numtheory):T:=proc(w) local x,y,z; x:=0; y:=w;
for z from 1 to ilog10(w)+1 do x:=10*x+(y mod 10); y:=trunc(y/10); od; x; end:
P:=proc(q) local k,n; for n from 1 to q do if n=T(phi(T(phi(n))))
then print(n); fi; od; end: P(10^12);

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

Extensions

a(9)-a(12) from Felix Fröhlich, Dec 30 2014