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 A378665 #16 Dec 06 2024 16:25:05
%S A378665 1,2,3,4,5,6,7,8,9,10,11,6,13,14,15,16,17,9,19,10,21,22,23,8,25,26,27,
%T A378665 28,29,15,31,32,33,34,35,9,37,38,39,10,41,21,43,44,45,46,47,16,49,50,
%U A378665 51,52,53,27,55,28,57,58,59,15,61,62,63,64,65,33,67,68,69,35,71,9,73,74,75,76,77,39,79,16,81,82,83,28
%N A378665 Greatest non-abundant divisor of n.
%C A378665 Largest term of A263837 that divides n.
%H A378665 Antti Karttunen, <a href="/A378665/b378665.txt">Table of n, a(n) for n = 1..20000</a>
%F A378665 a(n) = n / A378660(n).
%F A378665 a(n) >= A378664(n).
%e A378665 For n=10, which is a non-abundant number because sigma(10) = 18 < 2*10, its greatest divisor that is not abundant is 10 itself, thus a(10) = 10.
%e A378665 For n=12, which is an abundant number because sigma(12) = 28 > 2*12, its greatest divisor that itself is not abundant is 6, as sigma(6) = 12. Thus a(12) = 6.
%t A378665 a[n_]:=Max[Select[Divisors[n], DivisorSigma[1,#]<=2# &]]; Array[a,84] (* _Stefano Spezia_, Dec 06 2024 *)
%o A378665 (PARI)
%o A378665 A294935(n) = (sigma(n)<=(2*n));
%o A378665 A378665(n) = { fordiv(n,d,if(A294935(n/d), return(n/d))); (1); };
%Y A378665 Cf. A000203, A263837, A294935, A378660, A378664, A378735 [= a(A005101(n))].
%K A378665 nonn
%O A378665 1,2
%A A378665 _Antti Karttunen_, Dec 06 2024