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%I #17 Sep 08 2022 08:45:30
%S 6,15,18,21,33,39,45,51,54,57,63,69,87,93,99,111,117,123,129,135,141,
%T 153,159,162,171,177,183,189,201,207,213,219,237,249,261,267,279,291,
%U 297,303,309,321,327,333,339,351,369,381,387,393,405,411,417,423,447
%N Numbers of the form 3^k*p, where 1 <= k <= 6 and p is a prime different from 3.
%C Auxiliary sequence for A128694 which gives the number of groups of order a(n).
%C a(n) is a subset of the composite numbers m having the property that tau(3*m)=tau(m)+2, where tau(m)=A000005(m) (the number of divisors of m). All primes except 3 satisfy this property. - _Gary Detlefs_, Jan 25 2019
%H Klaus Brockhaus, <a href="/A128693/b128693.txt">Table of n, a(n) for n = 1..10000</a>
%e 135 = 3^3*5 is a term.
%o (Magma) [ n: n in [1..450] | #t eq 2 and ((t[1, 1] eq 2 and t[1, 2] eq 1 and t[2, 1] eq 3 and t[2, 2] le 6) or (t[1, 1] eq 3 and t[1, 2] le 6 and t[2, 2] eq 1)) where t is Factorization(n) ];
%Y Cf. A128694.
%K nonn
%O 1,1
%A _Klaus Brockhaus_, Mar 26 2007
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