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A176039 Primitive elements of A071562. 1
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 (list; graph; refs; listen; history; text; internal format)
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 an 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

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Last modified August 5 08:27 EDT 2021. Contains 346464 sequences. (Running on oeis4.)