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 A173997 Irregular triangular by columns derived from (1, 2, 3,...) * (1, 2, 3,...). 2
 1, 2, 3, 2, 4, 4, 5, 6, 3, 6, 8, 6, 7, 10, 9, 4, 8, 12, 12, 8, 9, 14, 15, 12, 5, 10, 16, 18, 16, 10, 11, 18, 21, 20, 15, 6, 12, 20, 24, 24, 20, 12 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Row sums = A006918: (1, 2, 5, 8, 14, 20, 30,...). LINKS FORMULA Given a (1, 2, 3,...) * (1, 2, 3,...) multiplication table; leftmost column of the triangle = (1, 2, 3,...). Then shift down each successive column of the array twice to get triangle A173997. EXAMPLE Given: ... 1,..2,..3,..4,..5,... 2,..4,..6,..8,.10,... 3,..6,..9,.12,.15,... 4,..8,.12,.16,.20,... ... After the shift twice operation, we obtain: ... 1; 2; 3, 2; 4, 4; 5, 6, 3; 6, 8, 6; 7, 10, 9, 4; 8, 12, 12, 8; 9, 14, 15, 12, 5; 10, 16, 18, 16, 10; 11, 18, 21, 20, 15, 6; 12, 20, 24, 24, 20, 12; ... CROSSREFS Cf. A006918 Sequence in context: A145394 A179806 A182762 * A029143 A153846 A284383 Adjacent sequences:  A173994 A173995 A173996 * A173998 A173999 A174000 KEYWORD nonn,tabf AUTHOR Gary W. Adamson, Mar 05 2010 STATUS approved

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Last modified February 19 10:18 EST 2019. Contains 320310 sequences. (Running on oeis4.)