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