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A033989 Write 0,1,2,... in a clockwise spiral on a square lattice, writing each digit at a separate lattice point, starting with 0 at the origin and 1 at x=0, y=-1; sequence gives the numbers on the negative x-axis. 16
0, 3, 1, 1, 3, 2, 7, 9, 1, 1, 6, 9, 4, 7, 9, 1, 2, 1, 2, 1, 6, 7, 4, 3, 6, 1, 2, 9, 5, 1, 1, 0, 9, 3, 1, 3, 6, 6, 1, 8, 6, 9, 2, 5, 0, 2, 2, 4, 6, 6, 2, 5, 6, 0, 3, 8, 9, 5, 3, 3, 6, 9, 4, 0, 5, 4, 4, 9, 8, 0, 5, 0, 4, 5, 5, 3, 3, 1, 6, 8, 5, 8, 6, 5, 1, 4, 7, 4, 9, 1, 8, 5, 1, 9, 9, 8, 6, 6, 9, 1, 1, 6, 4, 8, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 0..1000

FORMULA

a(n) = A033307(4*n^2-n-1) for n > 0. - Andrew Woods, May 20 2012

EXAMPLE

  2---3---2---4---2---5---2

  |                       |

  2   1---3---1---4---1   6

  |   |               |   |

  2   2   4---5---6   5   2

  |   |   |       |   |   |

  1   1   3   0   7   1   7

  |   |   |   |   |   |   |

  2   1   2---1   8   6   2

  |   |           |   |   |

  0   1---0---1---9   1   8

  |                   |   |

  2---9---1---8---1---7   2

We begin with the 0 and wrap the numbers 1 2 3 4 ... around it. Then the sequence is obtained by reading leftwards, starting from the initial 0. - Andrew Woods, May 20 2012

MATHEMATICA

nmax = 1000; A033307 = Flatten[IntegerDigits /@ Range[0, nmax^2+10*nmax]]; a[n_] := If[n==0, 0, A033307[[4n^2-n+1]]]; Table[a[n], {n, 0, nmax}] (* Jean-Fran├žois Alcover, Apr 23 2017, after Andrew Woods *)

PROG

(Haskell)

a033989 0 = 0

a033989 n = a033307 $ a185950 n  -- Reinhard Zumkeller, Aug 14 2013

CROSSREFS

Sequences based on the same spiral: A033953, A033988, A033990. Spiral without zero: A033952.

Other sequences from spirals: A001107, A002939, A007742, A033951, A033954, A033991, A002943, A033996, A033988.

Sequence in context: A229166 A143159 A184831 * A169941 A099545 A300867

Adjacent sequences:  A033986 A033987 A033988 * A033990 A033991 A033992

KEYWORD

nonn,base,easy,nice

AUTHOR

N. J. A. Sloane

EXTENSIONS

More terms from Andrew J. Gacek (andrew(AT)dgi.net)

Edited by Charles R Greathouse IV, Nov 01 2009

STATUS

approved

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Last modified October 21 20:51 EDT 2018. Contains 316428 sequences. (Running on oeis4.)