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 A115013 #17 Dec 09 2022 09:26:38 %S A115013 0,0,0,0,1,0,3,0,0,5,2,0,0,4,9,0,11,0,3,0,8,15,2,0,17,10,0,5,0,21,0, %T A115013 14,0,6,16,27,0,0,29,8,9,0,20,5,0,0,35,4,11,0,39,0,12,41,26,0,6,28,45, %U A115013 14,0,0,15,0,4,51,0,0,9,34,0,17,18,57,10,59,38,0,40,11,0,12,65,0,21,0,44,69,2 %N A115013 a(n) = difference between largest and smallest primes dividing the n-th squarefree integer (with a(1)=0). %F A115013 a(n) = A073482(n) - A073481(n). %e A115013 a(7)=3 because the 7th squarefree number is 10 = 2*5 and 5 - 2 = 3. %p A115013 with(numtheory): a:=proc(n) local FS: FS:=factorset(n): if abs(mobius(n))>0 then FS[nops(FS)]-FS[1] else fi end: seq(a(n),n=2..180); # _Emeric Deutsch_, Mar 07 2006 %K A115013 nonn %O A115013 1,7 %A A115013 _Leroy Quet_, Feb 28 2006 %E A115013 More terms from _Emeric Deutsch_, Mar 07 2006 %E A115013 a(1) = 0 inserted by _Georg Fischer_, Dec 09 2022