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 A109347 #15 Feb 16 2025 08:32:58
%S A109347 2,1,49,17,1441,19,37969,353,19729,421,24325489,481,609554401,10039,
%T A109347 216001,198593,381405156481,12979,9536162033329,288961,18306583,
%U A109347 6125659,5960417405949649,346561,103408180634401,152787181,3853528045489,179655841,93132223146359169121
%N A109347 Zsigmondy numbers for a = 5, b = 3: Zs(n, 5, 3) is the greatest divisor of 5^n - 3^n (A005058) that is relatively prime to 5^m - 3^m for all positive integers m < n.
%H A109347 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ZsigmondyTheorem.html">Zsigmondy's Theorem</a>
%o A109347 (PARI) rad(n) = factorback(factor(n)[, 1])
%o A109347 lista(nn) = {prad = 1; for (n=1, nn, val = 5^n-3^n; d = divisors(val); gd = 1; forstep(k=#d, 1, -1, if (gcd(d[k], prad) == 1, g = d[k]; break)); print1(g, ", "); prad = ra(prad*val););} \\ _Michel Marcus_, Nov 15 2016
%Y A109347 Cf. A064078, A064079, A064080, A064081, A064082, A064083, A109325, A109348, A109349.
%K A109347 nonn
%O A109347 1,1
%A A109347 _Jonathan Vos Post_, Aug 21 2005
%E A109347 Edited, corrected and extended by _Ray Chandler_, Aug 26 2005
%E A109347 Definition corrected by _Jerry Metzger_, Nov 04 2009
%E A109347 More terms from _Michel Marcus_, Nov 14 2016