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 A374609 #25 Jul 14 2024 13:47:59
%S A374609 1,2,5,14,714
%N A374609 Numbers k such that k*(k+1) is primorial (a term in A002110).
%C A374609 All terms are squarefree numbers (A005117).
%C A374609 a(n) >> exp(n/2); presumably finite. If a(6) exists then a(6) > 10^200000. - _Charles R Greathouse IV_, Jul 13 2024
%F A374609 From _Alois P. Heinz_, Jul 13 2024: (Start)
%F A374609 a(n) = A000194(A161620(n)).
%F A374609 A002378(a(n)) = A161620(n). (End)
%e A374609 714 is a term because 714*715 = 510510 = A002110(7) = 2*3*5*7*11*13*17.
%t A374609 nn = 1000; MapIndexed[Set[P[First[#2]], #1] &, FoldList[Times, Prime@ Range[nn]]]; Monitor[Reap[Do[(d = Floor@ Sqrt[#]; If[Divisible[#, d], Sow[d]]) &[P[i]], {i, nn}]][[-1, 1]], i] (* _Michael De Vlieger_, Jul 14 2024 *)
%Y A374609 Subsequence of A141399 and A007674.
%Y A374609 Cf. A000194, A002110, A002378, A005117, A161620 (resulting primorials).
%K A374609 nonn,hard
%O A374609 1,2
%A A374609 _David James Sycamore_ and _Michael De Vlieger_, Jul 13 2024