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A077661 Triangle read by rows in which the n-th row contains n smallest numbers not coprime to n; except first row = {1}.

%I A077661 #14 Jan 10 2025 20:28:53
%S A077661 1,2,4,3,6,9,2,4,6,8,5,10,15,20,25,2,3,4,6,8,9,7,14,21,28,35,42,49,2,
%T A077661 4,6,8,10,12,14,16,3,6,9,12,15,18,21,24,27,2,4,5,6,8,10,12,14,15,16,
%U A077661 11,22,33,44,55,66,77,88,99,110,121,2,3,4,6,8,9,10,12,14,15,16,18
%N A077661 Triangle read by rows in which the n-th row contains n smallest numbers not coprime to n; except first row = {1}.
%H A077661 Alois P. Heinz, <a href="/A077661/b077661.txt">Rows n = 1..200, flattened</a>
%e A077661 Triangle begins as:
%e A077661   1;
%e A077661   2,  4;
%e A077661   3,  6,  9;
%e A077661   2,  4,  6,  8;
%e A077661   5, 10, 15, 20, 25;
%e A077661   2,  3,  4,  6,  8,  9;
%e A077661   7, 14, 21, 28, 35, 42, 49;
%e A077661   ...
%t A077661 Join[{1},Table[Take[Select[Range[n^2],GCD[#,n]!=1 &],n],{n,2,13}]]//Flatten (* _Stefano Spezia_, Jan 10 2025 *)
%Y A077661 Cf. A077662, A077663.
%K A077661 nonn,look,tabl
%O A077661 1,2
%A A077661 _Amarnath Murthy_, Nov 14 2002
%E A077661 More terms from _Sascha Kurz_, Jan 27 2003