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 A385315 #74 Aug 22 2025 08:45:31 %S A385315 4,12,66,920,26,132,79,17958,53,693,4181,122160,29791,32318,971 %N A385315 Smallest number k such that both k^n - 1 and k^n + 1 have n prime factors, counted with repetitions. %H A385315 Jean-Marc Rebert, <a href="/A385315/a385315_2.pdf">Factorizations of k^n-1 and k^n+1</a> %e A385315 a(1) = 4, because 4^1 - 1 = 3 and 4^1 + 1 = 5, and no lesser number has this property. %e A385315 See the Links section for more examples. %o A385315 (PARI) a(n) = my(k=2, kn=k^n); while ((bigomega(kn-1)!=n) || (bigomega(kn+1)!=n), k++;kn=k^n); k; \\ _Michel Marcus_, Aug 18 2025 %Y A385315 Cf. A001222, A001358, A014612, A078840, A385591. %K A385315 nonn,more,changed %O A385315 1,1 %A A385315 _Jean-Marc Rebert_, Aug 12 2025