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 A381743 #10 Mar 06 2025 01:54:44 %S A381743 0,0,0,0,0,3,0,0,0,2,0,6,0,1,0,0,0,6,0,6,0,0,0,8,0,0,0,5,0,8,0,0,0,0, %T A381743 0,9,0,0,0,8,0,8,0,4,0,0,0,10,0,3,0,4,0,8,0,8,0,0,0,12,0,0,0,0,0,8,0, %U A381743 2,0,8,0,12,0,0,0,2,0,8,0,10,0,0,0,12,0,0 %N A381743 The number of divisors d of n such that d*n is abundant. %C A381743 The indices of records of this sequence are the highly composite numbers (A002182) without 2 and 4. %H A381743 Amiram Eldar, <a href="/A381743/b381743.txt">Table of n, a(n) for n = 1..10000</a> %F A381743 a(n) = A000005(n) if and only if n is abundant (A005101). %F A381743 a(n) = A000005(n) - 1 if and only if n is either 1, a perfect number (A000396), or in A341358. %F A381743 a(n) >= 1 if and only if n is in A381738. %F A381743 a(n) = 1 if and only if n is in A381742. %t A381743 a[n_] := DivisorSum[n, 1 &, DivisorSigma[-1, #*n] > 2 &]; Array[a, 100] %o A381743 (PARI) a(n) = sumdiv(n, d, sigma(d*n, -1) > 2); %Y A381743 Cf. A000005, A000396, A002182, A005101, A341358, A381738, A381742. %K A381743 nonn,easy %O A381743 1,6 %A A381743 _Amiram Eldar_, Mar 06 2025