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 A279211 Fill an array by antidiagonals upwards; in the n-th cell, enter the number of earlier cells that can be seen from that cell. 5
 0, 1, 2, 2, 4, 4, 3, 5, 6, 6, 4, 6, 8, 8, 8, 5, 7, 9, 10, 10, 10, 6, 8, 10, 12, 12, 12, 12, 7, 9, 11, 13, 14, 14, 14, 14, 8, 10, 12, 14, 16, 16, 16, 16, 16, 9, 11, 13, 15, 17, 18, 18, 18, 18, 18, 10, 12, 14, 16, 18, 20, 20, 20, 20, 20, 20, 11, 13, 15, 17 (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. LINKS Alec Jones, Table of n, a(n) for n = 0..5049 FORMULA T(x,y) = x+3*y if x >= y; T(x,y) = 2*(x+y) if x <= y. EXAMPLE The array begins: x\y| 0  1  2  3  4  5  6 ... ---+--------------------   0| 0  2  4  6  8 10 12 ...   1| 1  4  6  8 10 12 ...   2| 2  5  8 10 12 ...   3| 3  6  9 12 ...   4| 4  7 10 13 ...   5| 5  8 11 14 ...   6| ... ... For example, when we get to the antidiagonal that reads 4, 6, 8 ..., the reason for the 8 is that from that cell we can see two cells that have been filled in above it (containing 4 and 6), two cells to the northwest (0, 4), two cells to the west (2, 5), and two to the southwest (4, 6), which is 8 cells, so a(12) = 8. CROSSREFS Cf. A279966, A279967, A279212. See A280026, A280027 for similar sequences based on a spiral. Sequence in context: A196063 A205450 A215674 * A110545 A104798 A243238 Adjacent sequences:  A279208 A279209 A279210 * A279212 A279213 A279214 KEYWORD nonn,tabl AUTHOR N. J. A. Sloane, Dec 24 2016 EXTENSIONS More terms from Alec Jones, Dec 25 2016 STATUS approved

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Last modified May 31 22:11 EDT 2020. Contains 334756 sequences. (Running on oeis4.)