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 A013638 #15 Jul 08 2025 02:50:02
%S A013638 10,15,21,35,55,77,77,77,91,143,187,221,221,221,247,323,391,437,437,
%T A013638 437,551,667,667,667,667,667,713,899,1073,1147,1147,1147,1147,1147,
%U A013638 1271,1517,1517,1517,1591,1763,1927
%N A013638 a(n) = prevprime(n)*nextprime(n).
%H A013638 Reinhard Zumkeller, <a href="/A013638/b013638.txt">Table of n, a(n) for n = 3..10000</a>
%F A013638 a(n) = A151799(n)*A151800(n). - _Reinhard Zumkeller_, May 22 2015
%p A013638 [ seq(prevprime(i)*nextprime(i),i=3..70) ];
%t A013638 a[n_] := NextPrime[n, -1] NextPrime[n];
%t A013638 Table[a[n], {n, 3, 50}] (* _Jean-François Alcover_, Aug 02 2018 *)
%o A013638 (Haskell)
%o A013638 a013638 n = a151799 n * a151800 n -- _Reinhard Zumkeller_, May 22 2015
%Y A013638 Cf. A151799, A151800, A030664.
%K A013638 nonn
%O A013638 3,1
%A A013638 _N. J. A. Sloane_