login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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 |x-y|=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)=mn-Floor(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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 13 11:09 EST 2018. Contains 317133 sequences. (Running on oeis4.)