A176039 - OEIS

A176039

Primitive elements of A071562.

1, 2, 6, 9, 15, 20, 25, 28, 35, 42, 45, 49, 63, 66, 77, 88, 91, 99, 104, 110, 117, 121, 130, 143, 153, 156, 165, 169, 170, 187, 190, 195, 204, 209, 221, 228, 231, 238, 247, 255, 266, 272, 273, 276, 285, 289, 299, 304, 322, 323, 325, 342, 345, 350, 357, 361, 368

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OFFSET

1,2

COMMENTS

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

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

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.

LINKS

Table of n, a(n) for n=1..57.

EXAMPLE

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

CROSSREFS

Sequence in context: A049634 A120387 A325761 * A260699 A084265 A084140

Adjacent sequences: A176036 A176037 A176038 * A176040 A176041 A176042

KEYWORD

nonn

AUTHOR

Franklin T. Adams-Watters, Apr 07 2010

STATUS

approved