cp's OEIS Frontend

A080511 Triangle whose n-th row contains the least set (ordered lexicographically) of n distinct positive integers whose arithmetic mean is an integer.

%I A080511 #14 May 21 2016 03:04:43
%S A080511 1,1,3,1,2,3,1,2,3,6,1,2,3,4,5,1,2,3,4,5,9,1,2,3,4,5,6,7,1,2,3,4,5,6,
%T A080511 7,12,1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8,9,15,1,2,3,4,5,6,7,8,9,10,11,
%U A080511 1,2,3,4,5,6,7,8,9,10,11,18,1,2,3,4,5,6,7,8,9,10,11,12,13,1,2,3,4,5,6,7,8,9,10,11,12,13,21
%N A080511 Triangle whose n-th row contains the least set (ordered lexicographically) of n distinct positive integers whose arithmetic mean is an integer.
%C A080511 The n-th row is {1,2,...,n-1,x}, where x=n if n is odd, x=3n/2 if n is even.
%e A080511 Triangle starts:
%e A080511 1;
%e A080511 1, 3;
%e A080511 1, 2, 3;
%e A080511 1, 2, 3, 6;
%e A080511 1, 2, 3, 4, 5;
%e A080511 1, 2, 3, 4, 5, 9;
%e A080511 1, 2, 3, 4, 5, 6, 7;
%e A080511 1, 2, 3, 4, 5, 6, 7, 12;
%e A080511 ...
%p A080511 T:= proc(n) $1..n-1, `if`(irem(n, 2)=1, n, 3*n/2) end:
%p A080511 seq(T(n), n=1..20);  # _Alois P. Heinz_, Aug 29 2013
%t A080511 row[n_] := Append[Range[n - 1], If[OddQ[n], n, 3 n/2]];
%t A080511 Table[row[n], {n, 1, 20}] // Flatten (* _Jean-François Alcover_, May 21 2016 *)
%Y A080511 Cf. A080512, A008619, A080504, A080508.
%K A080511 nonn,tabl
%O A080511 1,3
%A A080511 _Amarnath Murthy_, Mar 20 2003