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 A072268 #17 Feb 01 2022 18:57:32 %S A072268 1,2,5,26,170,290,842,177242,160802,2810,78962,9223370,5033760602, %T A072268 2935496262242,2154284576409188208716642, %U A072268 1379590379356276893461978662419832989306970202,10320758390549056348725939119133160378521185060950774444682 %N A072268 a(0)=1; a(n+1) = 1 + f(a(n))^2, where f(x) is the largest prime factor of x (A006530). %C A072268 Is the sequence bounded? %C A072268 Essentially the same as A031439; a(n) = A031439(n-1)^2 + 1. - _Charles R Greathouse IV_, May 08 2009 %e A072268 Given a(5)=290: a(6) = 1 + lpf(a(5))^2 = 1 + lpf(290)^2 = 1 + 29^2 = 842. %p A072268 with(numtheory): a[0]:=1: a[1]:=2: for n from 2 to 20 do b:=factorset(a[n-1]): a[n]:=1+op(nops(b),b)^2: od: seq(a[n],n=0..20); # _Emeric Deutsch_, Feb 05 2006 %t A072268 NestList[1+FactorInteger[#][[-1,1]]^2&,1,17] (* _Harvey P. Dale_, Feb 01 2022 *) %Y A072268 Cf. A031439. %K A072268 nonn %O A072268 0,2 %A A072268 _Reinhard Zumkeller_, Jul 08 2002 %E A072268 More terms from _Emeric Deutsch_, Feb 05 2006 %E A072268 a(16) corrected by _T. D. Noe_, Nov 26 2007