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 A173997 Irregular triangular by columns derived from (1, 2, 3,...) * (1, 2, 3,...). 2

%I

%S 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,

%T 10,11,18,21,20,15,6,12,20,24,24,20,12

%N Irregular triangular by columns derived from (1, 2, 3,...) * (1, 2, 3,...).

%C Row sums = A006918: (1, 2, 5, 8, 14, 20, 30,...).

%F Given a (1, 2, 3,...) * (1, 2, 3,...) multiplication table; leftmost column

%F of the triangle = (1, 2, 3,...). Then shift down each successive column of

%F the array twice to get triangle A173997.

%e Given:

%e ...

%e 1,..2,..3,..4,..5,...

%e 2,..4,..6,..8,.10,...

%e 3,..6,..9,.12,.15,...

%e 4,..8,.12,.16,.20,...

%e ...

%e After the shift twice operation, we obtain:

%e ...

%e 1;

%e 2;

%e 3, 2;

%e 4, 4;

%e 5, 6, 3;

%e 6, 8, 6;

%e 7, 10, 9, 4;

%e 8, 12, 12, 8;

%e 9, 14, 15, 12, 5;

%e 10, 16, 18, 16, 10;

%e 11, 18, 21, 20, 15, 6;

%e 12, 20, 24, 24, 20, 12;

%e ...

%Y Cf. A006918

%K nonn,tabf

%O 1,2

%A _Gary W. Adamson_, Mar 05 2010

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Last modified January 24 01:05 EST 2020. Contains 331178 sequences. (Running on oeis4.)