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 A072680 #14 Sep 23 2018 20:56:57 %S A072680 0,0,2,0,2,0,4,4,4,0,2,0,4,4,4,0,2,0,4,4,4,0,6,6,6,6,6,0,2,0,6,6,6,6, %T A072680 6,0,4,4,4,0,2,0,4,4,4,0,6,6,6,6,6,0,6,6,6,6,6,0,2,0,6,6,6,6,6,0,4,4, %U A072680 4,0,2,0,6,6,6,6,6,0,4,4,4,0,6,6,6,6,6,0,8,8,8,8,8,8,8,0,4,4,4,0,2,0,4,4,4 %N A072680 Difference between (least prime >= n) and (largest prime <= n). %C A072680 a(n) = 0 iff n is prime. %H A072680 Antti Karttunen, <a href="/A072680/b072680.txt">Table of n, a(n) for n = 2..65537</a> %F A072680 a(n) = A007918(n) - A007917(n). %F A072680 a(n) = A057427(n - A007917(n)) * A001223(A049084(A007917(n))). %t A072680 f[n_]:=If[PrimeQ[n],0,NextPrime[n]-NextPrime[n,-1]];Array[f,110,2] (* _Harvey P. Dale_, Sep 22 2011 *) %o A072680 (MuPAD) numlib::prevprime(i)*(-1)-nextprime(i)*(-1)$ i = 2..106 // _Zerinvary Lajos_, Feb 26 2007 %o A072680 (PARI) A072680(n) = (nextprime(n) - precprime(n)); \\ _Antti Karttunen_, Sep 23 2018 %Y A072680 Cf. A007917, A007918, A013633, A072681, A097106. %K A072680 nonn %O A072680 2,3 %A A072680 _Reinhard Zumkeller_, Jul 01 2002