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 A007423 M0011 #27 Feb 21 2025 15:16:19 %S A007423 2,0,0,1,0,2,0,1,1,2,0,1,0,2,2,1,0,1,0,1,2,2,0,1,1,2,1,1,0,0,0,1,2,2, %T A007423 2,1,0,2,2,1,0,0,0,1,1,2,0,1,1,1,2,1,0,1,2,1,2,2,0,1,0,2,1,1,2,0,0,1, %U A007423 2,0,0,1,0,2,1,1,2,0,0,1,1,2,0,1,2,2,2,1,0,1,2,1,2,2,2,1,0,1,1,1 %N A007423 a(n) = mu(n) + 1, where mu is the Moebius function. %D A007423 G. H. Hardy and E. M. Wright, An Introduction to the Theory of Numbers. 3rd ed., Oxford Univ. Press, 1954, p. 234. %D A007423 K. Ireland and M. Rosen, A Classical Introduction to Modern Number Theory. Springer-Verlag, NY, 1982, p. 19. %D A007423 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A007423 Reinhard Zumkeller, <a href="/A007423/b007423.txt">Table of n, a(n) for n = 1..10000</a> %F A007423 a(n) = abs(a(n)). %p A007423 with(numtheory); A007423:=n->mobius(n)+1; seq(A007423(k), k=1..100); # _Wesley Ivan Hurt_, Oct 24 2013 %t A007423 MoebiusMu[Range[100]]+1 (* _Harvey P. Dale_, Nov 08 2011 *) %o A007423 (Haskell) %o A007423 a007423 = (+ 1) . a008683 -- _Reinhard Zumkeller_, Jul 30 2014 %o A007423 (PARI) a(n)=moebius(n)+1 \\ _Charles R Greathouse IV_, Feb 25 2018 %Y A007423 Cf. A008683 (mu). %K A007423 easy,nonn,nice %O A007423 1,1 %A A007423 _N. J. A. Sloane_