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 A174830 #32 Apr 25 2025 05:27:43
%S A174830 105,315,495,525,585,735,945,1155,1365,1485,1575,1755,1785,1995,2145,
%T A174830 2205,2415,2475,2625,2805,2835,2925,3045,3135,3255,3315,3465,3675,
%U A174830 3705,3795,3885,4095,4305,4455,4485,4515,4725,4785,4845,4935,5115,5145,5265
%N A174830 Odd numbers k such that k^2 is an abundant number.
%C A174830 Submitted at the suggestion of _T. D. Noe_.
%C A174830 For any number k, the abundance of k^2 is an odd number.
%C A174830 From _Amiram Eldar_, Jan 16 2025: (Start)
%C A174830 The least term that is not divisible by 5 is a(75) = 9009.
%C A174830 The least term that is not divisible by 3 is a(296889) = 37182145.
%C A174830 The least term that is coprime to 15 is 3909612711980232366109. (End)
%C A174830 The numbers of terms that do not exceed 10^k, for k = 3, 4, ..., are 7, 83, 792, 7988, 80082, 796603, 7952883, 79585351, ... . Apparently, the asymptotic density of this sequence exists and equals 0.00795... . - _Amiram Eldar_, Apr 25 2025
%H A174830 Amiram Eldar, <a href="/A174830/b174830.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from T. D. Noe)
%F A174830 a(n) = sqrt(A156942(n)). - _M. F. Hasler_, Jan 26 2020
%t A174830 fQ[n_] := Block[{ds = DivisorSigma[1, n^2] - 2 n^2}, ds > 0 && OddQ@ ds]; Select[ Range[1, 5353, 2], fQ@# &]
%o A174830 (PARI) is(n)=n%2 && sigma(n^2,-1)>2 \\ _Charles R Greathouse IV_, Feb 21 2017
%o A174830 (PARI) [2*k-1|k<-[1..6e3\2],sigma((2*k-1)^2,-1)>2] \\ _M. F. Hasler_, Jan 26 2020
%Y A174830 Cf. A005101, A005231, A033880, A156942.
%K A174830 nonn
%O A174830 1,1
%A A174830 _Robert G. Wilson v_, Mar 30 2010
%E A174830 Name corrected by _T. D. Noe_, Jul 09 2010