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A036798 Odd m such that there exists an even number k < m with phi(k) = phi(m). 11
105, 165, 195, 315, 495, 525, 585, 735, 825, 945, 975, 1155, 1365, 1485, 1575, 1755, 1785, 1815, 1995, 2145, 2205, 2415, 2475, 2535, 2625, 2805, 2835, 2925, 3003, 3045, 3135, 3255, 3315, 3465, 3675, 3705, 3795, 3885, 3927, 4095, 4125, 4305, 4389, 4455 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
These numbers m appear to satisfy cototient(m) > totient(m) or 2*phi(m) < m; they seem to be the missing terms mentioned in A067800. - Labos Elemer, May 08 2003
All elements in this sequence must have 2*phi(m) < m, but not the reverse. See A118700. - Franklin T. Adams-Watters, May 21 2006
LINKS
MAPLE
N:= 10^4: # to get all terms <= N
PhiE:= map(numtheory:-phi, [seq(i, i=2..N, 2)]):
A:= NULL:
for n from 1 to N by 2 do
t:= numtheory:-phi(n);
if 2*t < n and member(t, PhiE[1..(n-1)/2]) then A:= A, n fi;
od:
A; # Robert Israel, Jan 06 2017
MATHEMATICA
Select[ Range[1, 4483, 2], Mod[ #, EulerPhi[ # ]] != # - EulerPhi[ # ] &] (* Robert G. Wilson v, Jan 10 2004 *)
CROSSREFS
Cf. A091495 (Odd, squarefree n such that n/phi(n) > 2).
Sequence in context: A152940 A189936 A076762 * A119434 A091495 A256673
KEYWORD
nonn
AUTHOR
STATUS
approved

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Last modified March 28 14:21 EDT 2024. Contains 371254 sequences. (Running on oeis4.)