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 A089619 #18 Oct 29 2024 03:30:57
%S A089619 5,13,5,41,61,17,113,29,181,17,53,313,73,421,37,109,613,137,761,29,37,
%T A089619 1013,17,1201,1301,281,89,13,1741,1861,397,2113,449,2381,2521,41,97,
%U A089619 593,3121,193,53,3613,757,233,101,173,4513,941,29,5101,1061,149,229,457,101
%N A089619 a(n) = greatest prime factor of n^2 + (n+1)^2 for n >= 1.
%H A089619 Amiram Eldar, <a href="/A089619/b089619.txt">Table of n, a(n) for n = 1..10000</a>
%F A089619 a(n) = A006530(A001844(n)).
%e A089619 2*7^2 - 2*7 + 1 = 85 = 5*17, so a(7) = 17.
%t A089619 a[n_] := FactorInteger[n^2 + (n+1)^2][[-1, 1]]; Array[a, 60] (* _Amiram Eldar_, Oct 29 2024 *)
%o A089619 (PARI) xnpym1n(m) = { for(n=1,m, y = n^2+(n+1)^2; f = factor(y); l = length(component(f,1)); v = component(component(f,1),l); print1(v","); ) }
%Y A089619 Cf. A001844, A006530, A027861, A027862.
%K A089619 easy,nonn
%O A089619 1,1
%A A089619 _Cino Hilliard_, Dec 31 2003
%E A089619 Edited by _Ray Chandler_, Jan 03 2004
%E A089619 Offset corrected by _Georg Fischer_, May 27 2024