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 A381401 #10 Feb 25 2025 11:40:01
%S A381401 0,1,1,2,1,2,1,2,2,2,1,3,1,2,2,1,1,3,1,3,2,2,1,3,2,2,2,3,1,3,1,2,2,2,
%T A381401 2,4,1,2,2,3,1,3,1,3,3,2,1,2,2,3,2,3,1,3,2,3,2,2,1,4,1,2,3,1,2,3,1,3,
%U A381401 2,3,1,4,1,2,3,3,2,3,1,2,1,2,1,4,2,2,2,3,1,4
%N A381401 a(n) is the number of (possibly non-distinct) prime elements in the multiset of bases and exponents in the prime factorization of n.
%H A381401 Paolo Xausa, <a href="/A381401/b381401.txt">Table of n, a(n) for n = 1..10000</a>
%e A381401 a(144) = 3 because the prime factorization of 144 is 2^4*3^2 and the multiset of these bases and exponents is {2, 2, 3, 4}, containing 3 primes.
%t A381401 A381401[n_] := Count[FactorInteger[n], _?PrimeQ, {2}];
%t A381401 Array[A381401, 100]
%Y A381401 Cf. A106490, A349281, A381398, A381399.
%K A381401 nonn,easy
%O A381401 1,4
%A A381401 _Paolo Xausa_, Feb 24 2025