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A281880 Non-palindromic numbers k such that phi(k) | phi(R(k)), where R(k) is the digits reversal of k. 2
12, 15, 18, 19, 36, 37, 56, 124, 126, 132, 165, 168, 178, 189, 190, 192, 198, 199, 219, 234, 238, 298, 308, 348, 387, 396, 418, 427, 429, 468, 506, 518, 724, 756, 924, 1004, 1066, 1078, 1089, 1094, 1107, 1143, 1209, 1212, 1314, 1332, 1358, 1364, 1386, 1445, 1452 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Robert Israel, Table of n, a(n) for n = 1..1500

Paolo P. Lava, First 250 terms with the ratio phi(R(k))/phi(k)

EXAMPLE

a(1) = 12 because phi(21) / phi(12) = 12 / 4 = 3;

a(2) = 15 because phi(51) / phi(15) = 32 / 8 = 4;

a(3) = 18 because phi(81) / phi(18) = 54 / 6 = 9.

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 n<>T(n) then if type(phi(T(n))/phi(n), integer) then print(n); fi; fi; od; end: P(10^6);

MATHEMATICA

Select[Range@ 1500, Function[k, And[Reverse@ # != #, Divisible[EulerPhi[FromDigits@ Reverse@ #], EulerPhi@ k]] &@ IntegerDigits@ k]] (* Michael De Vlieger, Feb 04 2017 *)

CROSSREFS

Cf. A000010, A004086, A097647, A281879.

Sequence in context: A114443 A188766 A247542 * A153047 A265128 A243021

Adjacent sequences:  A281877 A281878 A281879 * A281881 A281882 A281883

KEYWORD

nonn,easy,base

AUTHOR

Paolo P. Lava, Feb 01 2017

STATUS

approved

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Last modified May 25 10:05 EDT 2022. Contains 354066 sequences. (Running on oeis4.)