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 A108540 #20 Feb 16 2025 08:32:58
%S A108540 6,15,77,187,589,851,1363,2183,2747,7303,10033,15229,16463,17201,
%T A108540 18511,27641,35909,42869,45257,53033,60409,83309,93749,118969,124373,
%U A108540 129331,156433,201563,217631,232327,237077,255271,270349,283663,303533,326423
%N A108540 Golden semiprimes: a(n)=p*q and abs(p*phi-q)<1, where phi = golden ratio = (1+sqrt(5))/2.
%H A108540 Amiram Eldar, <a href="/A108540/b108540.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from T. D. Noe)
%H A108540 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/GoldenRatio.html">Golden Ratio</a>
%H A108540 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Semiprime.html">Semiprime</a>
%F A108540 a(n) = A108541(n)*A108542(n) = A000040(k)*A108539(k) for some k.
%e A108540 589 = 19*31 and abs(19*phi - 31) = abs(30,7426... - 31) < 1, therefore 589 is a term.
%t A108540 f[p_] := Module[{x = GoldenRatio * p}, p1 = NextPrime[x, -1]; p2 = NextPrime[p1]; q = If[x - p1 < p2 - x, p1, p2]; If[Abs[q - x] < 1, q, 0]]; seq = {}; p=1; Do[p = NextPrime[p]; q = f[p]; If[q > 0, AppendTo[seq, p*q]], {100}]; seq (* _Amiram Eldar_, Nov 28 2019 *)
%Y A108540 Cf. A001622, A001358, A050508.
%K A108540 nonn
%O A108540 1,1
%A A108540 _Reinhard Zumkeller_, Jun 09 2005; revised Jun 13 2005
%E A108540 Corrected by _T. D. Noe_, Oct 25 2006