%I #9 Nov 18 2024 04:28:40
%S 504,864,960,1152,1260,2400,3276,3888,4992,6696,7020,7644,8892,9672,
%T 9984,11172,11200,11376,11616,11856,12936,13728,13888,14136,14280,
%U 15480,15876,15984,17808,19488,21336,22608,23688,24738,24840,25080
%N Numbers k such that sigma(x) = k has exactly 10 solutions.
%H Amiram Eldar, <a href="/A060666/b060666.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 504 = sigma(204) = sigma(220) = sigma(224) = sigma(246) = sigma(284) = sigma(286) = sigma(334) = sigma(415) = sigma(451) = sigma(504).
%t a = Table[ 0, {30000} ]; Do[ s = DivisorSigma[ 1, n ]; If[ s < 30001, a[ [ s ] ]++ ], {n, 1, 30000} ]; Select[ Range[ 30000 ], a[ [ # ] ] == 10 & ]
%o (PARI) is(k) = invsigmaNum(k) == 10 \\ _Amiram Eldar_, Nov 18 2024, using _Max Alekseyev_'s invphi.gp
%Y Cf. A000203.
%Y Number of solutions: A007369 (0), A007370 (1), A007371 (2), A007372 (3), A060660 (4), A060661 (5), A060662 (6), A060663 (7), A060664 (8), A060665 (9), this sequence (10), A060678 (11), A060676 (12).
%K nonn
%O 1,1
%A _Robert G. Wilson v_, Apr 18 2001