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

Offset: 1

Author

Franklin T. Adams-Watters, Apr 07 2010

Keywords

• nonn

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.

Examples

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