cp's OEIS Frontend

A290322 Sum modulo n of all units u in Z/nZ such that Phi(5,u) is a unit, where Phi is the cyclotomic polynomial.

%I A290322 #17 Jan 23 2024 08:41:54
%S A290322 1,0,0,4,0,0,0,0,9,1,0,0,0,3,0,0,0,0,8,0,12,0,0,20,0,0,0,0,18,1,0,24,
%T A290322 0,14,0,0,0,0,16,1,0,0,24,9,0,0,0,0,45,0,0,0,0,14,0,0,0,0,36,1,32,0,0,
%U A290322 13,24,0,0,0,14,1,0,0,0,15,0,28,0,0,32,0,42,0
%N A290322 Sum modulo n of all units u in Z/nZ such that Phi(5,u) is a unit, where Phi is the cyclotomic polynomial.
%C A290322 Conjecture: If n is divisible by 5 then a(n) > 0. - _Robert Israel_, Jan 23 2024
%H A290322 Robert Israel, <a href="/A290322/b290322.txt">Table of n, a(n) for n = 2..10000</a>
%p A290322 with(numtheory): m:=5: for n from 2 to 100 do S:={}: for a from 1 to n-1 do if gcd(a,n)=1 and gcd(cyclotomic(m,a),n)=1 then S:={op(S),a}: fi: od: print(sum(op(i,S),i=1..nops(S)) mod n): od:
%t A290322 Table[Mod[Total@ Select[Range[n - 1], CoprimeQ[#, n] && CoprimeQ[Cyclotomic[5, #], n] &], n], {n, 83}] (* _Michael De Vlieger_, Jul 29 2017 *)
%o A290322 (PARI) a(n) = sum(k=0, n-1, k*((gcd(n, k)==1) && (gcd(n, polcyclo(5, k))==1))) % n; \\ _Michel Marcus_, Jul 29 2017
%Y A290322 Cf. A058026, A289460.
%K A290322 nonn,look
%O A290322 2,4
%A A290322 _Joshua Harrington_, _Michael Mueller_, _Jordan Lenchitz_, _Tristan Phillips_, _Madison Wellen_, _Eric Jovinelly_, Jul 27 2017