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 A181851 Triangle read by rows: T(n,k) = Sum_{c in composition(n,k)} lcm(c). 3
 1, 2, 1, 3, 4, 1, 4, 8, 6, 1, 5, 20, 15, 8, 1, 6, 21, 50, 24, 10, 1, 7, 56, 66, 96, 35, 12, 1, 8, 60, 180, 160, 160, 48, 14, 1, 9, 96, 264, 432, 325, 244, 63, 16, 1, 10, 105, 510, 776, 892, 585, 350, 80, 18, 1, 11, 220, 567, 1704, 1835, 1668, 966, 480, 99, 20, 1 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Composition(n,k) is the set of the k-tuples of positive integers which sum to n (see A181842). Taking the example in A181842, T(6,2) = lcm(5,1) + lcm(4,2) + lcm(3,3) + lcm(2,4) + lcm(1,5) = 5+4+3+4+5 = 21. LINKS Alois P. Heinz, Rows n = 1..25, flattened EXAMPLE [1] 1 [2] 2 1 [3] 3 4 1 [4] 4 8 6 1 [5] 5 20 15 8 1 [6] 6 21 50 24 10 1 [7] 7 56 66 96 35 12 1 MAPLE with(combstruct): a181851_row := proc(n) local k, L, l, R, comp; R := NULL; for k from 1 to n do L := 0; comp := iterstructs(Composition(n), size=k): while not finished(comp) do l := nextstruct(comp); L := L + ilcm(op(l)); od; R := R, L; od; R end: MATHEMATICA c[n_, k_] := Permutations /@ IntegerPartitions[n, {k}] // Flatten[#, 1]&; t[n_, k_] := Total[LCM @@@ c[n, k]]; Table[t[n, k], {n, 1, 11}, {k, 1, n}] // Flatten (* Jean-François Alcover, Feb 05 2014 *) CROSSREFS Cf. A181849, A181850, A181853. Sequence in context: A361042 A072506 A188236 * A210231 A180378 A208341 Adjacent sequences: A181848 A181849 A181850 * A181852 A181853 A181854 KEYWORD nonn,tabl AUTHOR Peter Luschny, Dec 07 2010 STATUS approved

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Last modified February 29 02:52 EST 2024. Contains 370401 sequences. (Running on oeis4.)