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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.

%I A261987 #72 Nov 28 2015 13:43:40
%S A261987 4,8,9,25,26,27,91,92,93,95,115,116,117,119,121,527,529,531,532,533,
%T A261987 535,527,529,531,533,535,536,539,1331,1333,1334,1337,1339,1341,1343,
%U A261987 1345,1331,1333,1334,1337,1339,1341,1343,1345,1349
%N 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.
%C A261987 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.
%C A261987 In cases where multiple k-tuples satisfy the definition, the lexicographically earliest solution is chosen.
%H A261987 Max Barrentine, <a href="/A261987/b261987.txt">Table of n, a(n) for n = 1..189</a>
%e A261987 4;
%e A261987 8,   9;
%e A261987 25,  26,  27;
%e A261987 91,  92,  93,  95;
%e A261987 115, 116, 117, 119, 121;
%e A261987 527, 529, 531, 532, 533, 535;
%e A261987 ...
%Y A261987 Subsequence of A002808.
%Y A261987 First column is A262042.
%Y A261987 Cf. A264482.
%K A261987 tabl,nonn
%O A261987 1,1
%A A261987 _Max Barrentine_, Oct 02 2015, Nov 03 2015, Nov 05 2015