cp's OEIS Frontend

A361363 Primitive terms of A259850.

%I A361363 #7 Mar 09 2023 13:52:36
%S A361363 1,3,8,14,15,21,26,40,130,144,182,255,310,372,465,468,680,980,1524,
%T A361363 2170,2210,2418,2448,4030,4536,7008,7956,8890,9906,10220,10416,10668,
%U A361363 12648,16335,16660,17082,20216,24624,30800,36792,41106,44055,48400,65535,77112,78320,85120,97790,143000,149688
%N A361363 Primitive terms of A259850.
%C A361363 Terms k of A259850 such that no earlier term of A259850 has the same set of prime factors as k.
%C A361363 Numbers k such that k/phi(k) = sigma(x)/x for some x<=k, and there do not exist m and y with y <= m < k such that m has the same set of prime factors as k and sigma(y)/y = k/phi(k).
%e A361363 a(4) = 14 is a term because 14 = A259850(5) is the first term of A259850 whose set of prime factors is {2,7}.
%e A361363 28 = A259850(11) is not a term because it has the same set {2,7} of prime factors as 14.
%p A361363 R:= NULL: count:= 0: V:= {}: S:= {}:
%p A361363 for k from 1 while count < 50 do
%p A361363  V:= V union  {numtheory:-sigma(k)/k};
%p A361363  if member(k/numtheory:-phi(k), V) then
%p A361363    s:= numtheory:-factorset(k);
%p A361363      if not member(s,S) then
%p A361363       R:= R, k; count:= count+1; S:= S union {s}
%p A361363    fi fi;
%p A361363 od:
%p A361363 R;
%Y A361363 Cf. A000010, A000203, A259850.
%K A361363 nonn
%O A361363 1,2
%A A361363 _Robert Israel_, Mar 09 2023