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 A056140 #9 Mar 22 2020 04:01:52
%S A056140 -1,1,4,1,-6,-13,4,23,30,1,-18,-25,4,35,42,1,-30,-37,4,47,-22,-91,-42,
%T A056140 9,62,117,128,1,-112,-123,-58,9,78,149,98,-73,4,83,90,1,-78,-85,4,95,
%U A056140 -70,-187,-90,9,110,213,36,-211,-102,9,122,237,248,1,-232,-243
%N A056140 a(n) = n^2 - previousprime(n)*nextprime(n), for n>2.
%C A056140 a(n) is never 0.
%F A056140 a(n) = n^2-A007917(n-1)*A007918(n+1) = A000290(n)-A013638(n).
%e A056140 a(3)=3^2-2*5=-1, a(4)=4^2-3*5=1.
%t A056140 Table[n^2-NextPrime[n]NextPrime[n,-1],{n,3,80}] (* _Harvey P. Dale_, Aug 22 2011 *)
%o A056140 (PARI) a(n) = n^2 - precprime(n-1)*nextprime(n+1); \\ _Michel Marcus_, Mar 22 2020
%Y A056140 Cf. A056139, A056141.
%K A056140 easy,sign
%O A056140 3,3
%A A056140 _Henry Bottomley_, Jun 15 2000
%E A056140 More terms from _Harvey P. Dale_, Aug 22 2011