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Primitive elements of A071562.
1

%I #5 Oct 13 2023 06:48:21

%S 1,2,6,9,15,20,25,28,35,42,45,49,63,66,77,88,91,99,104,110,117,121,

%T 130,143,153,156,165,169,170,187,190,195,204,209,221,228,231,238,247,

%U 255,266,272,273,276,285,289,299,304,322,323,325,342,345,350,357,361,368

%N Primitive elements of A071562.

%C Members of A071562 which cannot be expressed as the product of two smaller elements of that sequence.

%C This definition is made to include 1; it would make about as much sense to exclude it.

%C This sequence includes all numbers of the form a*p, where p/2 < a <= p, for p prime. It also includes all p*q*r, where p, q, and r are odd primes, and p*q/2 < r < p*q. Similar but increasingly complex conditions can be made for products of more primes.

%e 4 is not in the sequence, because 4 = 2*2, and 2 is in A071562.

%K nonn

%O 1,2

%A _Franklin T. Adams-Watters_, Apr 07 2010