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 A383964 #30 Jun 24 2025 16:17:39 %S A383964 168,1320,3792,4968,7176,8184,14364,15240,20076,29904,30672,41952, %T A383964 48312,48768,54264,56856,57960,60144,64296,72996,73344,83328,90552, %U A383964 91512,99828,106020,110952,113280,114156,119016,128592,149292,150024,151272,157608,168588,175584,183240 %N A383964 Integers k such that there exists an integer 0<m<k such that (1/sigma(m)^2 + 1/sigma(k)^2)*(m+k)^2 = 1. %C A383964 The numbers m and k form a HM(2,1)-amicable pair (HM = harmonic mean). See Dimitrov link. %H A383964 S. I. Dimitrov, <a href="https://arxiv.org/abs/2408.07387">Generalizations of amicable numbers</a>, arXiv:2408.07387 [math.NT], 2024. %e A383964 (120, 168) is such a pair because (1/sigma(120)^2 + 1/sigma(168)^2)*(120+168)^2 = 1. %o A383964 (PARI) isok(k) = for(m=1, k-1, if((1/sigma(m)^2 + 1/sigma(k)^2)*(m+k)^2 == 1, return(m))); \\ _Michel Marcus_, May 16 2025 %Y A383964 Cf. A063990, A259180, A383239, A383483, A383484. %K A383964 nonn %O A383964 1,1 %A A383964 _S. I. Dimitrov_, May 16 2025 %E A383964 a(7) and a(9)-a(25) from _Michel Marcus_, May 16 2025 %E A383964 More terms from _David A. Corneth_, Jun 21 2025