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 A083720 #20 May 22 2024 16:56:48 %S A083720 1,1,2,1,6,1,30,1,2,3,210,1,2310,15,2,1,30030,1,510510,3,10,105, %T A083720 9699690,1,6,1155,2,15,223092870,1,6469693230,1,70,15015,6,1, %U A083720 200560490130,255255,770,3,7420738134810,5,304250263527210,105,2,4849845 %N A083720 Product of the primes less than the greatest prime factor of n but not dividing n. %C A083720 a(n) is squarefree, and all squarefree numbers appear infinitely often. a(m) = a(n) if and only if rad(m) = rad(n), where rad is A007947. - _Charles R Greathouse IV_, Apr 09 2024 %C A083720 Rad(n*a(n)) = A002110(A000720(A006530(n))) is the smallest primorial number divisible by rad(n). - _David James Sycamore_, May 15 2024 %H A083720 Michael De Vlieger, <a href="/A083720/b083720.txt">Table of n, a(n) for n = 1..2376</a> %F A083720 a(n) = A002110(A049084(A006530(n)))/A007947(n). %F A083720 a(A000040(k)) = A002110(k-1). %F A083720 a(n) = 1 iff n = m*A002110(k) and A006530(m) <= A000040(k). %t A083720 Array[Times @@ Complement[Prime@ Range@ PrimePi@ Last[#], #] &[FactorInteger[#][[All, 1]]] &, 46] (* _Michael De Vlieger_, Apr 09 2024 *) %Y A083720 Cf. A079067, A083722. %Y A083720 See the formula section for the relationships with A000040, A002110, A006530, A007947, A049084. %K A083720 nonn,easy %O A083720 1,3 %A A083720 _Reinhard Zumkeller_, May 04 2003 %E A083720 Edited by _Peter Munn_, Apr 09 2024