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 A135981 #9 Mar 14 2020 05:05:00
%S A135981 0,2,2,3,2,3,2,4,3,3,4,4,5,3,4,2,6,3,3,3,6,3,6,5,4,3,4,8,2,3,4,7,2,6,
%T A135981 3,7,6,4,3,9,2,7,5,7,3,6,6,8,4,6,2,11,3,6,7,3,8,2,7,4,9,3,12,3,5,7,7,
%U A135981 4,7,3,9,6,5,2,12,3,5,6,10,11,5,9,3,6,5,12,2,5,8,12
%N A135981 Number of distinct prime factors of A135972(n).
%H A135981 Amiram Eldar, <a href="/A135981/b135981.txt">Table of n, a(n) for n = 2..1193</a>
%F A135981 a(n) = A001221(A135972(n)) .
%e A135981 A135972(3) = 15 = 3*5 which has a(3)=2 distinct prime factors.
%t A135981 k = {}; Do[If[ ! PrimeQ[2^n - 1], c = FactorInteger[2^n - 1]; d = Length[c]; AppendTo[k, d]], {n, 1, 100}]; k
%Y A135981 Cf. A046051, A046053, A022307, A135972.
%K A135981 nonn
%O A135981 2,2
%A A135981 _Artur Jasinski_, Dec 09 2007
%E A135981 Offset set to 2, definition shortened - _R. J. Mathar_, Oct 01 2009