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 A219603 #13 Nov 18 2017 17:20:44 %S A219603 4,15,55,119,253,403,697,893,1357,1943,2263,3071,3977,4429,5123,6731, %T A219603 8083,9089,10519,11857,13067,15089,16351,18779,22019,23533,24823, %U A219603 27499,29321,31301,35941,40217,42881,46009,51703,53303,57619,61777,64963,69373,75001 %N A219603 a(n) = prime(n) * prime(2*n-1). %C A219603 A020639(a(n)) = A000040(n); A006530(a(n)) = A031368(n); %C A219603 a(n) is central term of row 2n-1 of semiprimes triangle (A087112). %H A219603 Reinhard Zumkeller, <a href="/A219603/b219603.txt">Table of n, a(n) for n = 1..10000</a> %F A219603 a(n) = A000040(n) * A031368(n). %o A219603 (Haskell) %o A219603 a219603 n = a000040 n * a031368 n %o A219603 (PARI) a(n)=prime(n) * prime(2*n-1) \\ _Charles R Greathouse IV_, Feb 07 2017 %Y A219603 Subsequence of A001358. %Y A219603 Cf. A006094. %K A219603 nonn %O A219603 1,1 %A A219603 _Reinhard Zumkeller_, Nov 25 2012