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 A063956 #28 Jan 26 2025 13:33:17
%S A063956 0,2,3,0,5,5,7,0,0,7,11,3,13,9,8,0,17,2,19,5,10,13,23,3,0,15,0,7,29,
%T A063956 10,31,0,14,19,12,0,37,21,16,5,41,12,43,11,5,25,47,3,0,2,20,13,53,2,
%U A063956 16,7,22,31,59,8,61,33,7,0,18,16,67,17,26,14,71,0,73,39,3,19,18,18,79,5,0
%N A063956 Sum of unitary prime divisors of n.
%H A063956 Amiram Eldar, <a href="/A063956/b063956.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from Harry J. Smith)
%F A063956 a(n*m) = a(n) + a(m) - a(gcd(n^2, m)) - a(gcd(n, m^2)) for all n and m > 0 (conjecture). - _Velin Yanev_, Feb 17 2019
%F A063956 From _Amiram Eldar_, Jul 24 2024: (Start)
%F A063956 a(n) = A008472(n) - A063958(n).
%F A063956 Additive with a(p^e) = p is e = 1, and 0 otherwise. (End)
%e A063956 The prime divisors of 420 = 2^2 * 3 * 5 * 7. Among them, those that have exponent 1 (i.e., unitary prime divisors) are {3, 5, 7}, so a(420) = 3 + 5 + 7 = 15.
%t A063956 Table[DivisorSum[n, # &, And[PrimeQ@ #, GCD[#, n/#] == 1] &], {n, 81}] (* _Michael De Vlieger_, Feb 17 2019 *)
%t A063956 f[p_, e_] := If[e == 1, p, 0]; a[1] = 0; a[n_] := Plus @@ f @@@ FactorInteger[n]; Array[a, 100] (* _Amiram Eldar_, Jul 24 2024 *)
%t A063956 Join[{0},Table[Total[Select[FactorInteger[n],#[[2]]==1&][[;;,1]]],{n,2,100}]] (* _Harvey P. Dale_, Jan 26 2025 *)
%o A063956 (PARI) { for (n=1, 1000, f=factor(n)~; a=0; for (i=1, length(f), if (f[2, i]==1, a+=f[1, i])); write("b063956.txt", n, " ", a) ) } \\ _Harry J. Smith_, Sep 04 2009
%Y A063956 Cf. A008472, A034387, A034444, A056169, A056170, A056171, A056172, A063958.
%K A063956 nonn,easy
%O A063956 1,2
%A A063956 _Labos Elemer_, Sep 04 2001
%E A063956 Example clarified by _Harvey P. Dale_, Jan 26 2025