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 A133801 #25 Feb 16 2025 08:33:06
%S A133801 1,1,2,2,2,3,2,3,3,3,3,5,2,3,4,5,3,6,3,5,4,5,3,7,4,3,6,6,4,8,4,6,5,6,
%T A133801 5,9,3,5,6,7,4,8,3,8,8,4,5,12,7,7,6,6,4,11,6,9,7,7,3,12,3,6,6,7,6,10,
%U A133801 4,9,6,8,2,12,5,6,9,8,7,12,4,11,9,6,5,14,6,4,8,12,4,16,5,7,7,8,6,15,4,10,8
%N A133801 Number of distinct prime divisors of 3^n - 1.
%H A133801 <a href="/A133801/b133801.txt">Table of n, a(n) for n = 1..690</a>
%H A133801 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PrimeFactor.html">Prime Factor</a>.
%F A133801 a(n) = omega(3^n - 1) = A001221(3^n - 1).
%e A133801 a(4) = omega(3^4 - 1) = omega(80) = omega(2^4 * 5) = 2.
%t A133801 Table[PrimeNu[3^n - 1], {n, 1, 50}] (* _G. C. Greubel_, May 21 2017 *)
%o A133801 (PARI) for(n = 1, 100, print1(omega(3^n - 1), ", "))
%Y A133801 Cf. A001221, A024023, A113913.
%K A133801 nonn
%O A133801 1,3
%A A133801 _Ryan Propper_, Jan 06 2008
%E A133801 Terms to a(660) in b-file from _Amiram Eldar_, Feb 03 2020
%E A133801 a(661)-a(690) in b-file from _Max Alekseyev_, May 22 2022