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 A245787 #24 Jan 10 2025 12:38:35 %S A245787 1,26208,56896,293760,997920,9694080,23569920,25159680,29669760, %T A245787 67858560,117849600,132723360,208565280,222963840,276756480,427714560, %U A245787 513786240,578672640,628992000,649503360,688279680,714954240,779950080,830269440,979102080,1037266560 %N A245787 Numbers n such that tau(n)*sigma(n) divides n^2. %C A245787 a(11) > 10^8. - _Derek Orr_, Aug 08 2014 %C A245787 Numbers n such that n^2 / (A000005(n) * A000203(n)) is an integer. %C A245787 Subsequence of A090777 (numbers n such that sigma(n) divides n^2). %C A245787 Sequence of numbers k(n) = n^2 / (tau(n) * sigma(n)): 1, 104, 889, 612, 945, 7344, … %H A245787 Jens Kruse Andersen, <a href="/A245787/b245787.txt">Table of n, a(n) for n = 1..47</a> %t A245787 a245787[n_Integer] := Select[Range[n], Divisible[#^2, DivisorSigma[0, #]*DivisorSigma[1, #]]&] (* _Michael De Vlieger_, Aug 09 2014 *) %o A245787 (Magma) [n: n in [1..1000000] | Denominator(n^2 / ((#[d: d in Divisors(n)])* SumOfDivisors(n))) eq 1]; %o A245787 (PARI) %o A245787 for(n=1,10^8,if(n^2%(numdiv(n)*sigma(n))==0,print1(n,", "))) \\ _Derek Orr_, Aug 08 2014 %Y A245787 Cf. A000005, A000203, A071707, A090777. %K A245787 nonn %O A245787 1,2 %A A245787 _Jaroslav Krizek_, Aug 08 2014 %E A245787 a(7)-a(10) from _Derek Orr_, Aug 08 2014 %E A245787 a(11)-a(26) from _Jens Kruse Andersen_, Aug 13 2014