cp's OEIS Frontend

A328174 a(n) is the least integer k such that sigma(k)/(d(k)*sopf(k)) = n where d=A000005, sigma=A000203 and sopf=A008472.

%I A328174 #6 Oct 06 2019 09:05:14
%S A328174 20,140,54,189,378,1365,540,945,1120,1755,1539,3465,500,1815,4256,
%T A328174 6384,14645,5280,1323,1029,864,23871,34579,12903,1715,2673,11934,5589,
%U A328174 106805,12285,5600,11625,21070,41915,4459,16905,61320,6615,11178,5145,110839,19656,109225
%N A328174 a(n) is the least integer k such that sigma(k)/(d(k)*sopf(k)) = n where d=A000005, sigma=A000203 and sopf=A008472.
%o A328174 (PARI) sopf(f) = sum(j=1, #f~, f[j, 1]); \\ A008472
%o A328174 isok(k, n) = my(fk=factor(k)); n*numdiv(fk)*sopf(fk) == sigma(fk);
%o A328174 a(n) = {my(k=1); while (!isok(k, n), k++); k;}
%Y A328174 Cf. A000005, A000203, A008472, A134382, A328051, A328052, A328175.
%K A328174 nonn
%O A328174 1,1
%A A328174 _Michel Marcus_, Oct 06 2019