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 A231821 #19 Nov 09 2024 10:03:53
%S A231821 4,2,2,3,2,4,2,3,3,4,2,3,2,4,4,3,2,3,2,3,4,4,2,3,3,4,3,3,2,2,2,3,4,4,
%T A231821 4,3,2,4,4,3,2,2,2,3,3,4,2,3,3,3,4,3,2,3,4,3,4,4,2,3,2,4,3,3,4,2,2,3,
%U A231821 4,2,2,3,2,4,3,3,4,2,2,3,3,4,2,3,4,4
%N A231821 a(n) = mu(n) + 3, where mu is the Mobius function (A008683).
%C A231821 If n is a prime or a semiprime, a(n) gives the number of divisors of n.
%H A231821 Antti Karttunen, <a href="/A231821/b231821.txt">Table of n, a(n) for n = 1..5000</a>
%H A231821 <a href="/index/Eu#epf">Index entries for sequences computed from exponents in factorization of n</a>
%e A231821 a(6) = 4; mu(6) + 3 = 1 + 3 = 4.
%p A231821 with(numtheory); a:=n->mobius(n)+3; seq(a(n), n=1..100);
%t A231821 Table[MoebiusMu[n] + 3, {n, 100}]
%o A231821 (PARI) a(n) = moebius(n) + 3; \\ _Michel Marcus_, Nov 14 2013
%o A231821 (Scheme)
%o A231821 (define (A231821 n) (+ 3 (A008683 n))) ;; _Antti Karttunen_, Jul 26 2017
%Y A231821 Cf. A008683, A228409.
%Y A231821 One more than A080847, two more than A007423.
%K A231821 nonn,easy
%O A231821 1,1
%A A231821 _Wesley Ivan Hurt_, Nov 13 2013