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 A128693 Numbers of the form 3^k*p, where 1 <= k <= 6 and p is a prime different from 3. 2
 6, 15, 18, 21, 33, 39, 45, 51, 54, 57, 63, 69, 87, 93, 99, 111, 117, 123, 129, 135, 141, 153, 159, 162, 171, 177, 183, 189, 201, 207, 213, 219, 237, 249, 261, 267, 279, 291, 297, 303, 309, 321, 327, 333, 339, 351, 369, 381, 387, 393, 405, 411, 417, 423, 447 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Auxiliary sequence for A128694 which gives the number of groups of order a(n). 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 LINKS Klaus Brockhaus, Table of n, a(n) for n = 1..10000 EXAMPLE 135 = 3^3*5 is a term. PROG (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) ]; CROSSREFS Cf. A128694. Sequence in context: A099535 A302296 A070999 * A105285 A138922 A044058 Adjacent sequences:  A128690 A128691 A128692 * A128694 A128695 A128696 KEYWORD nonn AUTHOR Klaus Brockhaus, Mar 26 2007 STATUS approved

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Last modified November 28 18:22 EST 2021. Contains 349415 sequences. (Running on oeis4.)