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A128853 a(n) is the number of positive divisors of n which are coprime to phi(n) = A000010(n). 1
1, 2, 2, 1, 2, 2, 2, 1, 1, 2, 2, 2, 2, 2, 4, 1, 2, 1, 2, 2, 2, 2, 2, 2, 1, 2, 1, 2, 2, 4, 2, 1, 4, 2, 4, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 4, 2, 2, 1, 2, 2, 2, 2, 2, 4, 2, 2, 2, 1, 4, 4, 2, 2, 4, 4, 2, 1, 2, 2, 2, 2, 4, 2, 2, 2, 1, 2, 2, 2, 4, 2, 4, 2, 2, 2, 4, 2, 2, 2, 4, 2, 2, 1, 2, 1, 2, 4, 2, 2, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
LINKS
EXAMPLE
12 is coprime to 4 positive integers (1,5,7 and 11) which are <= 12; so phi(12)=4. There are 2 divisors (1 and 3) of 12 that are coprime to 4. So a(12) = 2.
MAPLE
with(numtheory): a:=proc(n) local div, ct, j: div:=divisors(n): ct:=0: for j from 1 to tau(n) do if igcd(div[j], phi(n))=1 then ct:=ct+1 else fi od: ct; end: seq(a(n), n=1..140); # Emeric Deutsch, Apr 17 2007
MATHEMATICA
Table[Total[Boole[CoprimeQ[Divisors[n], EulerPhi[n]]]], {n, 120}] (* Harvey P. Dale, Oct 18 2020 *)
PROG
(PARI) A128853(n) = { my(ph=eulerphi(n)); sumdiv(n, d, (1==(gcd(d, ph)))); }; \\ Antti Karttunen, Sep 27 2018
CROSSREFS
Sequence in context: A214517 A230594 A072463 * A136165 A134193 A230259
KEYWORD
nonn
AUTHOR
Leroy Quet, Apr 16 2007
EXTENSIONS
More terms from Emeric Deutsch, Apr 17 2007
STATUS
approved

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Last modified March 28 18:04 EDT 2024. Contains 371254 sequences. (Running on oeis4.)