A261987 Triangle read by rows: row n lists the set of n coprime composite numbers that minimizes the difference between first and last terms, and then minimizes the average of the terms.

4, 8, 9, 25, 26, 27, 91, 92, 93, 95, 115, 116, 117, 119, 121, 527, 529, 531, 532, 533, 535, 527, 529, 531, 533, 535, 536, 539, 1331, 1333, 1334, 1337, 1339, 1341, 1343, 1345, 1331, 1333, 1334, 1337, 1339, 1341, 1343, 1345, 1349

Offset

1,1

Comments

The minimal set of the (k+n)th row is determined by the minimal k-tuple coprime to the n-th primorial, where every prime <= to the n-th prime must be a factor of some number in the set. E.g., the sixth row must consist of numbers congruent to 5, 7, 11 and 13 mod 6, as well as one term with a factor of 2 and another with a factor of 3.

In cases where multiple k-tuples satisfy the definition, the lexicographically earliest solution is chosen.

Links

Max Barrentine, Table of n, a(n) for n = 1..189

Example

4;
8,   9;
25,  26,  27;
91,  92,  93,  95;
115, 116, 117, 119, 121;
527, 529, 531, 532, 533, 535;
...

Crossrefs

Subsequence of A002808.

First column is A262042.

Cf. A264482.

Sequence in context: A035326 A180865 A063907 * A158340 A350014 A259183

Adjacent sequences: A261984 A261985 A261986 * A261988 A261989 A261990

Keyword

tabl,nonn

Author

Max Barrentine, Oct 02 2015, Nov 03 2015, Nov 05 2015

Status

approved