A033989 - OEIS

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.

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-François 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: A143159 A324079 A184831 * A307501 A169941 A099545

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