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 A341318 Lower triangular table of products in the semigroup S = {(0,0), (i,j): i >= j >= 1} (see Comments for precise definition), read by rows. 4
 0, 0, 1, 0, 2, 7, 0, 3, 8, 10, 0, 4, 16, 17, 37, 0, 5, 17, 19, 38, 40, 0, 6, 18, 21, 39, 42, 45, 0, 7, 29, 30, 67, 68, 69, 121, 0, 8, 30, 32, 68, 70, 72, 122, 124, 0, 9, 31, 34, 69, 72, 75, 123, 126, 129, 0, 10, 32, 36, 70, 74, 78, 124, 128, 132, 136, 0, 11, 46, 47, 106, 107, 108, 191, 192, 193, 194, 301 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 0,5 COMMENTS Consider the semigroup S consisting of the pairs (0,0) and {(i,j): i >= j >= 1}, with componentwise products. Label the elements 0 = (0,0), 1 = (1,1), 2 = (2,1), 3 = (2,2), 4 = (3,1), 5 = (3,2), 6 = (3,3), 7 = (4,1), ... The triangle gives T(n,k) = label of product of n-th and k-th elements, for n>=k>=0. See A341317 for further information, including a Maple program. LINKS Alois P. Heinz, Rows n = 0..200, flattened EXAMPLE Triangle begins: 0, [0] 1, [0, 1] 2, [0, 2, 7] 3, [0, 3, 8, 10] 4, [0, 4, 16, 17, 37] 5, [0, 5, 17, 19, 38, 40] 6, [0, 6, 18, 21, 39, 42, 45] 7, [0, 7, 29, 30, 67, 68, 69, 121] 8, [0, 8, 30, 32, 68, 70, 72, 122, 124] 9, [0, 9, 31, 34, 69, 72, 75, 123, 126, 129] 10, [0, 10, 32, 36, 70, 74, 78, 124, 128, 132, 136] ... MAPLE t:= n-> n*(n-1)/2: f:= n-> ceil((sqrt(1+8*n)-1)/2): g:= n-> (x-> [x, n-t(x)][])(f(n)): T:= (n, k)-> (h-> t(h[1]*h[3])+h[2]*h[4])(map(g, [n, k])): seq(seq(T(n, k), k=0..n), n=0..12);  # Alois P. Heinz, Feb 17 2021 CROSSREFS Cf. A341317, A341706. Main diagonal gives A341736. Sequence in context: A188737 A200680 A260129 * A332324 A101689 A175292 Adjacent sequences:  A341315 A341316 A341317 * A341319 A341320 A341321 KEYWORD nonn,tabl AUTHOR N. J. A. Sloane, Feb 17 2021 STATUS approved

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Last modified April 19 04:54 EDT 2021. Contains 343105 sequences. (Running on oeis4.)