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A354530 Numbers k such that k^2 is a minimal number; numbers k whose square is in A007416.

%I A354530 #28 Sep 04 2022 12:35:29
%S A354530 1,2,4,6,8,12,24,30,32,36,60,64,72,96,120,180,192,210,216,256,288,360,
%T A354530 420,480,512,576,768,840,864,900,960,1080,1260,1440,1536,1680,1728,
%U A354530 1800,2048,2304,2520,2880,3360,3840,4320,4608,4620,5400,6144,6300,6720,6912,7200,7560
%N A354530 Numbers k such that k^2 is a minimal number; numbers k whose square is in A007416.
%C A354530 Numbers k such that there is no m < k^2 such that d(m) = d(k^2), d = A000005. Since only squares have an odd number of divisors, also numbers k such that there is no m < k such that d(m^2) = d(k^2).
%H A354530 David A. Corneth, <a href="/A354530/b354530.txt">Table of n, a(n) for n = 1..14008</a> (first 310 terms from Jianing Song, terms <= 10^20).
%F A354530 d(a(n)^2) = A166722(n).
%e A354530 8 is a term since 8^2 = 64 has 7 divisors and no smaller number (smaller square) has that many divisors.
%o A354530 (PARI) lista(nn) = {v = []; for (n=1, nn, d = numdiv(n^2); if (! vecsearch(v, d), print1(n, ", "); v = Set(concat(v, d))); ); } \\ from _Michel Marcus_'s program for A166721
%Y A354530 Cf. A007416, A000005, A025487.
%Y A354530 Square root of A166721. Also A016017 or A071571 sorted.
%Y A354530 Cf. also A166722.
%K A354530 nonn,easy
%O A354530 1,2
%A A354530 _Jianing Song_, Aug 16 2022