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 A367503 #20 Jun 06 2025 18:53:21
%S A367503 1,3,4,3,6,12,8,3,4,8,2,12,4,14,14,3,8,12,10,8,12,6,4,12,6,12,4,14,10,
%T A367503 22,2,3,8,14,18,12,8,20,16,8,2,26,4,6,14,12,8,12,8,8,12,12,4,12,12,14,
%U A367503 20,20,10,22,2,6,12,3,14,24,8,14,16,24,2,12,4,14,14,20
%N A367503 Sum of the final digits of the squarefree divisors of n.
%C A367503 Inverse Möbius transform of mu(n)^2 * (n mod 10). - _Wesley Ivan Hurt_, Jun 21 2024
%H A367503 Robert Israel, <a href="/A367503/b367503.txt">Table of n, a(n) for n = 1..10000</a>
%F A367503 a(n) = Sum_{d|n} mu(d)^2 * (d mod 10).
%e A367503 a(10) = 8. The squarefree divisors of 10 are 1, 2, 5, 10 and the sum of their final digits is 1 + 2 + 5 + 0 = 8.
%p A367503 f:= proc(n) local t; add(t mod 10, t = map(convert,combinat:-powerset(numtheory:-factorset(n)),`*`)) end proc:
%p A367503 map(f, [$1..100]); # _Robert Israel_, Nov 21 2023
%t A367503 Table[DivisorSum[n, MoebiusMu[#]^2*Mod[#, 10] &], {n, 100}]
%t A367503 Table[Total[Mod[Select[Divisors[n],SquareFreeQ],10]],{n,100}] (* _Harvey P. Dale_, Jun 06 2025 *)
%o A367503 (PARI) a(n) = sumdiv(n, d, if (issquarefree(d), d%10)); \\ _Michel Marcus_, Nov 21 2023
%Y A367503 Cf. A005117 (squarefree numbers), A010879 (final digit of n), A367466 (sum of the final digits of the divisors of n), A371925 (numbers that occur in this sequence).
%K A367503 nonn,easy,base
%O A367503 1,2
%A A367503 _Wesley Ivan Hurt_, Nov 20 2023