A396178 - OEIS

A396178

Lexicographically earliest sequence of the form 1, 2, followed by squarefree semiprimes (A006881), with the property that (a) for all k>=0, a(k) shares a factor with exactly k other terms, and (b) for all k >= 1, a(k) is divisible by a prime which does not divide any earlier term.

1, 2, 6, 15, 35, 55, 91, 119, 209, 253, 319, 403, 481, 533, 559, 799, 901, 1003, 1037, 1139, 1349, 1387, 1501, 1577, 1691, 2231, 2323, 2369, 2461, 2507, 2599, 3683, 3799, 3973, 4031, 4321, 4379, 4553, 5053, 5177, 5363, 5549, 5611, 5921, 5983, 7289, 7363, 7807, 8251

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OFFSET

0,2

COMMENTS

This is the same as A395795 except that the latter has a(1) = 4. Although the latter sequence has historical precedence, its definition was initially conjectural, and the present sequence is both simpler and belongs to a family of sequences (which is why the database now contains both versions).

LINKS

Table of n, a(n) for n=0..48.

CROSSREFS

Cf. A006881, A392373, A395360, A395795.

Sequence in context: A340779 A073838 A337646 * A014303 A076060 A126764

Adjacent sequences: A396175 A396176 A396177 * A396179 A396180 A396181

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, May 26 2026

STATUS

approved