This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A381741 #9 Mar 06 2025 01:44:40
%S A381741 6,10,14,105,286,374,418,442,506,2145,2805,3135,3315,3705,3795,4485,
%T A381741 4785,4845,5115,5655,6045,6105,6765,7095,7755,8745,9735,10065,11362,
%U A381741 14326,14858,15314,17342,18278,18538,18734,19778,20026,20254,21242,22126,22678,23218
%N A381741 Squarefree numbers k such that k^2 is abundant, and d^2 is nonabundant for any proper divisor d of k.
%C A381741 The primitive terms of A381740. Each term of A381740 is a multiple of a term in this sequence.
%H A381741 Amiram Eldar, <a href="/A381741/b381741.txt">Table of n, a(n) for n = 1..10000</a>
%t A381741 q[k_] := SquareFreeQ[k] && DivisorSigma[-1, k^2] > 2 && AllTrue[Divisors[k], DivisorSigma[-1, #^2] <= 2 || # == k &]; Select[Range[24000], q]
%o A381741 (PARI) is1(k) = {my(f = factor(k)); if(!issquarefree(f), 0, prod(i = 1, #f~, f[i,2] *= 2); sigma(f, -1) > 2);}
%o A381741 isok(k) = if(!is1(k), 0, fordiv(k, d, if(d < k && is1(d), return(0))); 1);
%Y A381741 Intersection of A005117 and A381739.
%Y A381741 Subsequence of A381738 and A381740.
%Y A381741 Cf. A005101, A263837.
%K A381741 nonn,easy
%O A381741 1,1
%A A381741 _Amiram Eldar_, Mar 06 2025