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 A054009 #13 Oct 27 2023 22:00:46
%S A054009 0,0,0,0,0,0,2,1,1,0,2,0,2,0,0,0,3,0,0,0,1,0,3,1,2,0,3,0,2,0,2,0,1,2,
%T A054009 4,0,2,0,5,0,0,0,4,0,1,0,3,1,0,0,2,0,5,1,0,0,1,0,5,0,2,3,4,2,3,0,3,0,
%U A054009 0,0,6,0,2,0,1,2,1,0,8,1,1,0,7,1,2,0,4,0,2,1,2,0,1,2,8,0,3,4,4,0,4,0,6,0,1
%N A054009 n read modulo (number of proper divisors of n).
%F A054009 a(n) = n mod (tau(n) - 1), for n>1.
%p A054009 [ seq( i mod (tau(i) - 1), i=2..150) ];
%t A054009 Table[Mod[n,DivisorSigma[0,n]-1],{n,2,110}] (* _Harvey P. Dale_, Dec 05 2015 *)
%o A054009 (PARI) a(n) = n % (numdiv(n) - 1); \\ _Michel Marcus_, Nov 21 2019
%o A054009 (Python)
%o A054009 from sympy import divisor_count
%o A054009 def A054009(n): return n%(divisor_count(n)-1) # _Chai Wah Wu_, Mar 14 2023
%Y A054009 Cf. A000005, A032741, A054008.
%K A054009 nonn
%O A054009 2,7
%A A054009 _Asher Auel_, Jan 12 2000