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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
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
Sequence in context: A113622 A069215 A115921 * A072395 A113781 A299450
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 February 24 01:16 EST 2024. Contains 370288 sequences. (Running on oeis4.)