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A251808 Numbers n such that if m = reverse(phi(n)) then n = reverse(phi(m)). 0
1, 21, 63, 291, 2744, 2991, 6102, 6711, 46676013, 69460293, 272543398, 896172631 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

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

LINKS

Table of n, a(n) for n=1..12.

EXAMPLE

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

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

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);

PROG

(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

CROSSREFS

Cf. A000010, A072395.

Sequence in context: A113622 A069215 A115921 * A072395 A113781 A299450

Adjacent sequences:  A251805 A251806 A251807 * A251809 A251810 A251811

KEYWORD

nonn,base,more

AUTHOR

Paolo P. Lava, Dec 09 2014

EXTENSIONS

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

STATUS

approved

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Last modified September 24 23:13 EDT 2020. Contains 337325 sequences. (Running on oeis4.)