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 A055769 #17 Sep 18 2024 02:36:26 %S A055769 1,2,2,3,5,5,5,5,11,11,11,11,11,11,23,23,29,29,29,29,29,29,41,41,41, %T A055769 41,41,53,53,53,53,53,53,53,53,53,53,53,83,83,89,89,89,89,89,89,89,89, %U A055769 113,113,113,113,113,113,113,131,131,131,131,131,131,131,131,131,131,131 %N A055769 Largest prime dividing phi of the n-th primorial. %H A055769 Reinhard Zumkeller, <a href="/A055769/b055769.txt">Table of n, a(n) for n = 1..10000</a> %F A055769 a(n) = A006530(A000010(A002110(n))). [corrected by _Amiram Eldar_, Sep 18 2024] %F A055769 a(n) = A006530(A005867(n)). - _Reinhard Zumkeller_, May 01 2013 %e A055769 While the largest prime factors of 10th, 100th or 1000th primorials are 29, 541, 7919, those of their totients are 11, 251, 3911, respectively. %t A055769 Map[FactorInteger[EulerPhi@ #][[-1, 1]] &, FoldList[#1 #2 &, Prime@ Range@ 66]] (* _Michael De Vlieger_, Oct 26 2017 *) %o A055769 (Haskell) %o A055769 a055769 = a006530 . a005867 -- _Reinhard Zumkeller_, May 01 2013 %o A055769 (PARI) gpf(n)=my(f=factor(n)[,1]); f[#f] %o A055769 a(n)=my(p=prime(n),q=1); while(2*q+1<p, q=max(gpf(p-1),q); p=precprime(p-1)); if(n==2, 2, q) \\ _Charles R Greathouse IV_, Dec 03 2014 %Y A055769 Cf. A000010, A002110, A005867, A055768. %K A055769 nonn %O A055769 1,2 %A A055769 _Labos Elemer_, Jul 12 2000