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 A075730 #14 Mar 22 2021 06:04:49
%S A075730 81,225,441,625,1089,1225,1521,2401,2601,3025,3249,4225,4761,5929,
%T A075730 7225,7569,8281,8649,9025,12321,13225,14161,14641,15129,16641,17689,
%U A075730 19881,20449,21025,24025,25281,25921,28561,31329,33489,34225,34969,40401
%N A075730 Squares of odd semiprimes A046315, odd numbers divisible by exactly 2 primes (counted with multiplicity).
%H A075730 Amiram Eldar, <a href="/A075730/b075730.txt">Table of n, a(n) for n = 1..10000</a>
%F A075730 Sum_{n>=1} 1/a(n) = P(2)^2/2 + P(4)/2 - P(2)/4 = 0.02769857933..., where P is the prime zeta function. - _Amiram Eldar_, Mar 22 2021
%e A075730 9 is odd and divisible by 3 (twice) and 9*9=81.
%e A075730 15 is odd and divisible by 3 and 5 and 15*15=225.
%p A075730 readlib(issqr): ts_kv_sp_lih := proc(n); if (numtheory[bigomega](n)=4 and type(n,odd)='true' and issqr(n)='true') then RETURN(n); fi; end: seq(ts_kv_sp_lih(i), i=1..100000);
%t A075730 Select[Range[1, 201, 2], PrimeOmega[#] == 2 &]^2 (* _Amiram Eldar_, Mar 22 2021 *)
%Y A075730 Equals A046315(n)^2.
%K A075730 easy,nonn
%O A075730 1,1
%A A075730 _Jani Melik_, Oct 07 2002
%E A075730 Checked by _Zak Seidov_, Mar 08 2006