OFFSET
1,2
COMMENTS
In the first 1000 terms, only 69 are odd. - Harvey P. Dale, Jul 16 2016
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
The sum of the positive divisors of 12 is 1+2+3+4+6+12 = 28. There are 2 positive divisors (1 and 3) of 12 which are coprime to 28. 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], sigma(n))=1 then ct:=ct+1 else ct:=ct fi od: ct: end: seq(a(n), n=1..140); # Emeric Deutsch, May 05 2007
MATHEMATICA
pdc[n_]:=Module[{s=DivisorSigma[1, n]}, Count[Divisors[n], _?(CoprimeQ[ #, s]&)]]; Array[pdc, 110] (* Harvey P. Dale, Jul 16 2016 *)
PROG
(PARI) a(n)=my(s=sigma(n)); sumdiv(n, d, gcd(s, d)==1) \\ Charles R Greathouse IV, Feb 19 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Leroy Quet, Apr 16 2007
EXTENSIONS
More terms from Emeric Deutsch, May 05 2007
STATUS
approved