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 A063826 Let 1, 2, 3, 4 represent moves to the right, down, left and up; this sequence describes the movements in the clockwise square spiral (a.k.a. Ulam Spiral). 34
 1, 2, 3, 3, 4, 4, 1, 1, 1, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Sequence starts with 1, 2, 3, then can be broken into groups of 8n+4 members, so if n is incremented, starting at 1, the groups follow the following pattern: 3 occurs at the beginning of the group, 4 then occurs 2n times, 1 occurs 2n+1 times, 2 occurs 2n+1 times, 3 occurs 2n+1 times; so each group has 8n+4 terms. Simpler description: Groups of 2*(2n-1) + 2*(2n) = 8n - 2 terms, n = 1, 2, 3, ..., consisting of 2n-1 times 1, then 2n-1 times 2; then 2n times 3, then 2n times 4. The n-th group starts at index (4n - 6)n + 2 and ends at index (4n + 2)n - 1. - M. F. Hasler, Aug 08 2020 LINKS Harry J. Smith, Table of n, a(n) for n = 0..1000 D. Alpern, Ulam's Spiral Adrian J. F. Leatherland, The mysterious Ulam spiral phenomenon FORMULA 1 <= a(n) <= 4 with a(n) == floor(sqrt(4n + 1)) (mod 4). - M. F. Hasler, Aug 08 2020 EXAMPLE Breaking into the groups, we have: 1, 2, 3 n=1: 3, 4, 4, 1, 1, 1, 2, 2, 2, 3, 3, 3, n=2: 3, 4, 4, 4, 4, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3 n=3: 3, 4, 4, 4, 4, 4, 4, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3 and so on. The spiral of numbers which shows in which order the steps in direction right, down, left and up are made, is depicted for example in sequence A174344. - M. F. Hasler, Aug 08 2020 MATHEMATICA a[n_] := Mod[Floor[Sqrt[4*n + 1]] + 3, 4] + 1; Table[a[n], {n, 0, 104}] (* Jean-François Alcover, Nov 30 2016 adapted from PARI *) Join[{1, 2, 3}, Flatten[Table[{{3}, PadRight[{}, 2n, 4], Table[PadRight[{}, 2n+1, k], {k, 3}]}, {n, 5}]]] (* Harvey P. Dale, Jun 29 2019 *) PROG (PARI) A063826(n)=(sqrtint(4*n+1)+3)%4+1 \\ To see the terms: apply(A063826, [0..99]) CROSSREFS Cf. A000267, A174344. Sequence in context: A096827 A298321 A226142 * A320120 A152983 A331377 Adjacent sequences:  A063823 A063824 A063825 * A063827 A063828 A063829 KEYWORD easy,nice,nonn AUTHOR Wai Ha Lee (Wainson(AT)hotmail.com), Aug 20 2001 STATUS approved

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Last modified September 25 00:02 EDT 2020. Contains 337333 sequences. (Running on oeis4.)