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 A290742 Orbit of word "1" under the 3-shift tag system over the alphabet {1,2} defined in the Comments. 4
 1, 12, 112, 2112, 21221222, 212221221222, 2212212221221222, 22122212212221221222, 222122122212212221221222, 1221222122122212212221221222, 12221221222122122212212222112, 212212221221222122122221122112, 2122212212221221222211221121221222 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS This tag system maps a word w over {1,2} to w', where if w begins with 1, w' is obtained by appending 2112 to w and deleting the first three letters, or if w begins with 2, w' is obtained by appending 1221222 to w and deleting the first three letters. This is a 3-shift version of a 5-shift tag system studied in [De Mol, p. 307]. LINKS Michael S. Branicky, Table of n, a(n) for n = 1..322 Liesbeth De Mol, Tracing unsolvability. A historical, mathematical and philosophical analysis with a special focus on tag systems, Ph.D. Thesis, Universiteit Gent. See page 307. MAPLE with(StringTools); f1:=proc(w) local L, t2, t1, ws, w2; t1:="2112"; t2:="1221222"; ws:=convert(w, string); if ws[1]="1" then w2:=Join([ws, t1], ""); else w2:=Join([ws, t2], ""); fi; L:=length(w2); if L <= 3 then return(-1); fi; w2[4..L]; end; # and apply f1 repeatedly to "1" PROG (Python) from itertools import islice def agen(w="1"): while True: yield int(w) w += ("2112" if w[0] == "1" else "1221222") w = w[3:] print(list(islice(agen(), 13))) # Michael S. Branicky, Mar 15 2022 CROSSREFS Cf. A284116, A290741. Sequence in context: A265948 A016152 A089700 * A268767 A221368 A083767 Adjacent sequences: A290739 A290740 A290741 * A290743 A290744 A290745 KEYWORD nonn AUTHOR N. J. A. Sloane, Aug 11 2017 STATUS approved

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Last modified October 2 08:18 EDT 2023. Contains 365831 sequences. (Running on oeis4.)