%I #14 Apr 15 2024 03:32:43
%S 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,8,19,20,21,22,23,24,25,26,
%T 27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,
%U 8,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72
%N a(n) is the smallest k such that k*n has exactly as many divisors as n^2.
%H Amiram Eldar, <a href="/A093616/b093616.txt">Table of n, a(n) for n = 1..10000</a>
%F A000005(a(n)*n) = A000005(n^2) and A000005(m*n) <> A000005(n^2) for m < a(n).
%F a(A093617(n)) < n, a(A093618(n)) = n.
%t a[n_] := For[k = 1, True, k++, If[DivisorSigma[0, k*n] == DivisorSigma[0, n^2], Return[k]]]; Array[a, 72] (* _Jean-François Alcover_, Aug 14 2014 *)
%o (PARI) a(n) = {my(k = 1, d = numdiv(n^2)); while(numdiv(k*n) != d, k++); k;} \\ _Amiram Eldar_, Apr 15 2024
%Y Cf. A000005, A000290, A048691, A093617, A093618.
%K nonn
%O 1,2
%A _Reinhard Zumkeller_, Apr 06 2004