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 A380847 #11 Feb 09 2025 06:54:15
%S A380847 1800,3720,7560,15240,20832,30600,42336,61320,85344,109320,116040,
%T A380847 122760,171360,218760,238920,245640,343392,346440,395880,437640,
%U A380847 462600,484680,491400,580680,687456,854760,875400,896520,917880,925320,950520,954120,976200,982920,1011720
%N A380847 Numbers k such that A380845(k) = 3*k.
%C A380847 Analogous to triperfect numbers (A005820) with A380845 instead of A000203.
%C A380847 All the terms are 3-abundant numbers (A068403), because A380845(k) <= A000203(k) with equality only when k is a power of 2, and powers of 2 are deficient numbers (A005100).
%H A380847 Amiram Eldar, <a href="/A380847/b380847.txt">Table of n, a(n) for n = 1..10000</a>
%e A380847 1800 is a term since A380845(18) = 5400 = 3 * 1800.
%t A380847 q[k_] := Module[{h = DigitCount[k, 2, 1]}, DivisorSum[k, # &, DigitCount[#, 2, 1] == h &] == 3*k]; Select[Range[10^6], q]
%o A380847 (PARI) isok(k) = {my(h = hammingweight(k)); sumdiv(k, d, d*(hammingweight(d) == h)) == 3*k;}
%Y A380847 Cf. A000203, A005100, A005820, A380845, A380846, A380848.
%Y A380847 Subsequence of A068403.
%K A380847 nonn,base,easy
%O A380847 1,1
%A A380847 _Amiram Eldar_, Feb 05 2025