

A143979


Rectangular array R by antidiagonals: label each unit square in the first quadrant lattice by its northeast vertex (x,y) and mark squares having xy=0(mod 3); then R(m,n) is the number of UNmarked squares in the rectangle [0,m]x[0,n].


3



0, 1, 1, 2, 2, 2, 2, 4, 4, 2, 3, 5, 6, 5, 3, 4, 6, 8, 8, 6, 4, 4, 8, 10, 10, 10, 8, 4, 5, 9, 12, 13, 13, 12, 9, 5, 6, 10, 14, 16, 16, 16, 14, 10, 6, 6, 12, 16, 18, 20, 20, 18, 16, 12, 6, 7, 13, 18, 21, 23, 24, 23, 21, 18, 13, 7, 8, 14, 20, 24, 26, 28, 28, 26, 24, 20, 14, 8, 8, 16, 22, 26, 30
(list;
table;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,4


COMMENTS

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..83.


FORMULA

R(m,n)=mnFloor(2mn/3).


EXAMPLE

Northwest corner:
0 1 2 2 3 4 4
1 2 4 5 6 8 9
2 4 6 8 10 12 14
2 5 8 10 13 16 18
3 6 10 13 16 20 23


CROSSREFS

Cf. A143974, A143976, A143977.
Sequence in context: A237120 A060369 A179004 * A034877 A224516 A023161
Adjacent sequences: A143976 A143977 A143978 * A143980 A143981 A143982


KEYWORD

nonn,tabl


AUTHOR

Clark Kimberling, Sep 06 2008


STATUS

approved



