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A143977 Rectangular array R by antidiagonals: label each unit square in the first quadrant lattice by its northeast vertex (x,y) and mark squares having |x-y|=0(mod 3); then R(m,n) is the number of marked squares in the rectangle [0,m] X [0,n]. 4
1, 1, 1, 1, 2, 1, 2, 2, 2, 2, 2, 3, 3, 3, 2, 2, 4, 4, 4, 4, 2, 3, 4, 5, 6, 5, 4, 3, 3, 5, 6, 7, 7, 6, 5, 3, 3, 6, 7, 8, 9, 8, 7, 6, 3, 4, 6, 8, 10, 10, 10, 10, 8, 6, 4, 4, 7, 9, 11, 12, 12, 12, 11, 9, 7, 4, 4, 8, 10, 12, 14, 14, 14, 14, 12, 10, 8, 4, 5, 8, 11, 14, 15, 16, 17, 16, 15, 14, 11, 8, 5, 5, 9 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

1,5

COMMENTS

Diagonals: A008810, A007984, A000212, A128422;

Rows and columns: A002264, A004523, A000027, A004772, A047212, et al.;

Rows numbered 3,6,9,12,15,... are, except for initial terms, multiples of (1,2,3,4,5,6,7,...)=A000027.

LINKS

Table of n, a(n) for n=1..93.

FORMULA

R(m,n) = Floor(2*m*n/3).

EXAMPLE

Northwest corner:

  1  1  1  2  2  2  3

  1  2  2  3  4  4  5

  1  2  3  4  5  6  7

  2  3  4  6  7  8 10

  2  4  5  7  9 10 12

CROSSREFS

Cf. A143974, A143977, A143979.

Sequence in context: A230198 A024939 A024937 * A115265 A105223 A025859

Adjacent sequences:  A143974 A143975 A143976 * A143978 A143979 A143980

KEYWORD

nonn,tabl

AUTHOR

Clark Kimberling, Sep 06 2008

STATUS

approved

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Last modified May 18 10:19 EDT 2021. Contains 343995 sequences. (Running on oeis4.)