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A247080 Numbers whose Euler totient is the reverse of the sum of its aliquot parts. 1
2, 735, 7665, 11505, 42630, 64578, 3440409, 11263073973 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Value of x such that phi(x) = Rev(sigma(x) - x).

a(9) > 2*10^11. - Hiroaki Yamanouchi, Nov 22 2014

a(9) > 10^13. - Giovanni Resta, Aug 26 2019

LINKS

Table of n, a(n) for n=1..8.

EXAMPLE

phi(2) = 1 and sigma(2) - 2 = 1.

phi(735) = 336 and sigma(735) - 735 = 633.

phi(7665) = 3456 and sigma(7665) - 7665 = 6543.

MAPLE

with(numtheory): T:=proc(w) local x, y, z; x:=w; y:=0;

for z from 1 to ilog10(x)+1 do

y:=10*y+(x mod 10); x:=trunc(x/10); od; y; end:

P:=proc(q) local n; for n from 1 to q do

if phi(n)=T(sigma(n)-n) then print(n); fi; od; end: P(10^9);

MATHEMATICA

Select[Range[10^6], EulerPhi[#] == FromDigits[Reverse[IntegerDigits[DivisorSigma[1, #] - #]]] &] (* Michael De Vlieger, Jan 29 2015 *)

PROG

(PARI) rev(n) = subst(Polrev(digits(n)), x, 10);

isok(n) = rev(sigma(n)-n) == eulerphi(n); \\ Michel Marcus, Jan 29 2015

CROSSREFS

Cf. A000010, A001065, A069225, A254320.

Sequence in context: A109949 A151591 A252986 * A145124 A102969 A179960

Adjacent sequences:  A247077 A247078 A247079 * A247081 A247082 A247083

KEYWORD

nonn,base,more

AUTHOR

Paolo P. Lava, Nov 17 2014

EXTENSIONS

a(7)-a(8) from Hiroaki Yamanouchi, Nov 22 2014

STATUS

approved

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Last modified August 11 15:12 EDT 2020. Contains 336428 sequences. (Running on oeis4.)