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%I #18 Dec 26 2024 03:53:15
%S 1,3,7,13,15,31,39,57,63,91,93,121,127,133,171,183,195,217,255,307,
%T 363,381,399,403,465,511,549,553,741,781,819,847,855,871,921,931,961,
%U 993,1023,1093,1143,1209,1281,1407,1651,1659,1723,1729,1767,1815,1893,1953
%N Odd values of the sum-of-divisors function sigma (A000203) (without repetitions).
%C That is, the odd values produced by the sigma function.
%C Odd terms of A002191. - _Michel Marcus_, Jun 10 2014
%H Giovanni Resta, <a href="/A060657/b060657.txt">Table of n, a(n) for n = 1..10000</a>
%H Max Alekseyev, <a href="https://oeis.org/wiki/User:Max_Alekseyev/gpscripts">PARI/GP Scripts for Miscellaneous Math Problems</a> (invphi.gp).
%e a(7) = 39 because sigma(18) = 1+2+3+6+9+18 = 39, an odd number.
%t nn = 2000; Union[Select[DivisorSigma[1, Range[nn]], OddQ[#] && # <= nn &]] (* _Harvey P. Dale_, Mar 12 2011 *)
%o (PARI) is(k) = k % 2 && invsigmaNum(k) > 0; \\ _Amiram Eldar_, Dec 26 2024, using _Max Alekseyev_'s invphi.gp
%Y Cf. A000203, A002191, A007369.
%K nonn
%O 1,2
%A _Robert G. Wilson v_, Apr 18 2001
%E Name edited by _Giovanni Resta_, Jan 08 2020