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 A033988 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 positive y-axis. 16
 0, 5, 1, 4, 3, 7, 8, 0, 4, 7, 7, 1, 2, 6, 2, 1, 8, 7, 4, 2, 6, 1, 8, 9, 2, 7, 6, 0, 6, 5, 1, 2, 0, 4, 1, 5, 8, 5, 1, 8, 8, 8, 2, 1, 2, 3, 2, 4, 9, 0, 2, 8, 9, 9, 3, 3, 2, 0, 3, 7, 9, 3, 4, 2, 8, 8, 4, 7, 1, 5, 5, 3, 7, 4, 5, 9, 7, 5, 6, 5, 9, 8, 7, 1, 5, 3, 7, 8, 4, 0, 8, 5, 6, 9, 9, 3, 1, 0, 9, 8, 1, 1, 6, 9, 9 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS In other words, write 0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 ... in a clockwise spiral, starting with the 0 and taking the first step south; the sequence is then picked out from the resulting spiral by starting at the origin and moving north. LINKS Andrew Woods, Table of n, a(n) for n = 0..1000 FORMULA a(n) = A033307(4*n^2 + n - 1) for n > 0. - Andrew Woods, May 18 2012 EXAMPLE 1---3---1---4---1 | | 2 4---5---6 5 | | | | 1 3 0 7 1 | | | | | 1 2---1 8 6 | | | 1---0---1---9 1 . We begin with the 0 and wrap the numbers 1 2 3 4 ... around it. Then the sequence is obtained by reading vertically upwards, starting from the initial 0. MATHEMATICA nmax = 105; 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 24 2017, after Andrew Woods *) CROSSREFS Sequences based on the same spiral: A033953, A033989, A033990. Spiral without zero: A033952. Other sequences from spirals: A001107, A002939, A007742, A033951, A033954, A033991, A002943, A033996. Cf. A033307. Sequence in context: A254247 A216606 A351789 * A229200 A200421 A019977 Adjacent sequences: A033985 A033986 A033987 * A033989 A033990 A033991 KEYWORD nonn,easy,base AUTHOR N. J. A. Sloane EXTENSIONS More terms from Andrew Gacek (andrew(AT)dgi.net) Edited by Jon E. Schoenfield, Aug 12 2018 STATUS approved

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Last modified February 21 02:30 EST 2024. Contains 370219 sequences. (Running on oeis4.)