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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
OFFSET
1,1
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
KEYWORD
nonn,easy,base
AUTHOR
Paolo P. Lava, Feb 01 2017
STATUS
approved