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 A117183 #27 Jun 25 2025 03:32:32 %S A117183 2,2,3,2,2,2,2,2,5,3,2,2,2,2,2,3,2,7,2,2,2,2,2,3,2,2,2,3,2,2,3,2,2,2, %T A117183 2,2,2,3,2,2,2,2,2,3,2,11,2,5,2,2,2,3,2,2,2,3,2,2,2,3,2,2,2,2,2,13,3, %U A117183 2,5,2,2,2,2,3,2,2,2,2,2,3,2,2,2,2,2,3,2,2,2,2,2,2,3,2,5,2,2,2,2,2,3,2,2,2 %N A117183 a(n) = smallest prime dividing n-th nonsquarefree positive integer. %H A117183 Amiram Eldar, <a href="/A117183/b117183.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from Harvey P. Dale) %F A117183 a(n) = A020639(A013929(n)). %e A117183 12, the 4th nonsquarefree positive integer, is 2^2 * 3. 2 is the smallest prime dividing 12. So a(4) = 2. %p A117183 with(numtheory): a:=proc(n) if mobius(n)=0 then op(1,factorset(n)) fi end: seq(a(n),n=1..345); # _Emeric Deutsch_ %t A117183 FactorInteger[ # ][[1, 1]] & /@ Select[ Range@252, !SquareFreeQ@# &] (* _Robert G. Wilson v_, Mar 06 2006 *) %t A117183 FactorInteger[#][[1,1]]&/@DeleteCases[Range[300],_?SquareFreeQ] (* _Harvey P. Dale_, Jun 02 2017 *) %o A117183 (PARI) list(lim) = apply(x -> factor(x)[1,1], select(x -> !issquarefree(x), vector(lim, i, i))); \\ _Amiram Eldar_, Jun 25 2025 %Y A117183 Cf. A013929, A020639, A073481, A115074, A115090. %K A117183 nonn %O A117183 1,1 %A A117183 _Leroy Quet_, Mar 01 2006 %E A117183 More terms from _Emeric Deutsch_ and _Robert G. Wilson v_, Mar 06 2006