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 A131225 Triangle read by rows: T(n,k)=2k - [1+(-1)^(n-k)]/2 (1<=k<=n). 2
 1, 2, 3, 1, 4, 5, 2, 3, 6, 7, 1, 4, 5, 8, 9, 2, 3, 6, 7, 10, 11, 1, 4, 5, 8, 9, 12, 13, 2, 3, 6, 7, 10, 11, 14, 15, 1, 4, 5, 8, 9, 12, 13, 16, 17, 2, 4, 6, 8, 10, 11, 14, 15, 18, 19 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Row sums = A035608: (1, 5, 10, 18, 27, 39,...). LINKS FORMULA 2*A002260 - A128174, as infinite lower triangular matrices; where A002260 = (1; 1,2; 1,2,3;...) and A128174 = (1; 0,1; 1,0,1;...). EXAMPLE First few rows of the triangle are: 1; 2, 3; 1, 4, 5; 2, 3, 6, 7; 1, 4, 5, 8, 9; 2, 3, 6, 7, 10, 11; 1, 4, 5, 8, 9, 12, 13; ... MAPLE T := proc (n, k) options operator, arrow; 2*k-1/2-(1/2)*(-1)^(n-k) end proc: for n to 10 do seq(T(n, k), k = 1 .. n) end do; # yields sequence in triangular form - Emeric Deutsch, Jul 09 2007 CROSSREFS Cf. A002260, A128174, A035608. Sequence in context: A094137 A038802 A092942 * A221919 A137671 A026370 Adjacent sequences:  A131222 A131223 A131224 * A131226 A131227 A131228 KEYWORD nonn,tabl AUTHOR Gary W. Adamson, Jun 20 2007 STATUS approved

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Last modified May 19 09:55 EDT 2013. Contains 225429 sequences.