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A279212 Fill an array by antidiagonals upwards; in the top left cell enter a(0)=1; thereafter, in the n-th cell, enter the sum of the entries of those earlier cells that can be seen from that cell. 5
1, 1, 2, 2, 6, 11, 4, 15, 39, 72, 8, 37, 119, 293, 543, 16, 88, 330, 976, 2364, 4403, 32, 204, 870, 2944, 8373, 20072, 37527, 64, 464, 2209, 8334, 26683, 74150, 176609, 331072, 128, 1040, 5454, 22579, 79534, 246035, 673156, 1595909, 2997466, 256, 2304, 13176, 59185, 226106, 762221, 2303159, 6231191, 14721429, 27690124 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

"That can be seen from" means "that are on the same row, column, diagonal, or antidiagonal as".

Inspired by A279967.

Conjecture: Every column has a finite number of odd entries, and every row and diagonal have an infinite number of odd entries. - Peter Kagey, Mar 28 2020. The conjecture about columns is true, see that attached pdf file from Alec Jones.

The "look" keyword refers to Peter Kagey's bitmap. - N. J. A. Sloane, Mar 29 2020

LINKS

Alec Jones and Alois P. Heinz, Antidiagonals n = 0..200, flattened (first 20 antidiagonals from Alec Jones)

Alec Jones, Proof that columns have finitely many odd entries.

Peter Kagey, Bitmap showing parity of first 1024 rows and 512 columns. (Odd values are white; even values are black.)

EXAMPLE

The array begins:

    1    2   11    72   543   4403  37527  331072 2997466 ...

    1    6   39   293  2364  20072 176609 1595909 ...

    2   15  119   976  8373  74150 673156 ...

    4   37  330  2944 26683 246035 ...

    8   88  870  8334 79534 ...

   16  204 2209 22579 ...

   32  464 5454 ...

   64 1040 ...

  128 ...

  ...

For example, when we get to the antidiagonal that reads 4, 15, 39, ..., the reason for the 39 is that from that cell we can see one cell that has been filled in above it (containing 11), one cell to the northwest (2), two cells to the west (1, 6), and two to the southwest (4, 15), for a total of a(8) = 39.

CROSSREFS

Cf. A279966, A279967, A279211.

See A280026, A280027 for similar sequences based on a spiral.

Sequence in context: A103774 A036052 A308260 * A299018 A269830 A275312

Adjacent sequences:  A279209 A279210 A279211 * A279213 A279214 A279215

KEYWORD

nonn,tabl,look,changed

AUTHOR

N. J. A. Sloane, Dec 24 2016

STATUS

approved

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Last modified April 9 04:05 EDT 2020. Contains 333343 sequences. (Running on oeis4.)