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 A361520 #40 May 07 2023 14:55:20 %S A361520 2,3,13,89,809,349,409,144541,10446133981,1361264878245241, %T A361520 4398505263882824939701,17847523009215848981, %U A361520 512996953133650208042047593649109478833 %N A361520 a(n) is the greatest prime factor of a(n-2)^2 + a(n-1)^2 where a(1)=2 and a(2)=3. %H A361520 Sebastian F. Orellana, <a href="/A361520/b361520.txt">Table of n, a(n) for n = 1..15</a> %p A361520 A[1]:= 2: A[2]:= 3: %p A361520 for n from 3 to 15 do A[n]:= max(numtheory:-factorset(A[n-2]^2 + A[n-1]^2)) od: %p A361520 seq(A[],n=1..15); # _Robert Israel_, Mar 17 2023 %t A361520 a[1] = 2; a[2] = 3; a[n_] := a[n] = FactorInteger[a[n - 1]^2 + a[n - 2]^2][[-1, 1]]; Array[a, 14] (* _Amiram Eldar_, Mar 14 2023 *) %Y A361520 Cf. A006530, A113494, A175723. %K A361520 nonn %O A361520 1,1 %A A361520 _Sebastian F. Orellana_, Mar 14 2023