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A035485
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Card on top of deck at n-th stage of R. K. Guy's shuffling problem.
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21
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1, 2, 3, 1, 6, 5, 9, 1, 4, 2, 16, 10, 12, 14, 23, 16, 18, 20, 17, 27, 30, 33, 38, 10, 14, 37, 32, 6, 11, 19, 53, 37, 25, 21, 12, 34, 38, 8, 50, 48, 46, 14, 18, 23, 47, 53, 84, 52, 31, 49, 1, 51, 91, 61, 42, 79, 4, 29, 6, 49, 26, 23, 115, 4, 70, 93, 109, 11, 16, 19, 49, 18, 124, 97, 70, 10, 134, 111, 7, 38, 14, 79, 11, 129
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OFFSET
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0,2
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COMMENTS
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At n-th step, pick up top n cards and interlace them with the next n.
Here is the deck after steps 0,1,2,3,4,5:
1,2,3,4,5,6,7,...
2,1,3,4,5,6,7,...
3,2,4,1,5,6,7,...
1,3,5,2,6,4,7,8,9,...
6,1,4,3,7,5,8,2,9,10,...
It is conjectured that eventually every number appears on top of the deck.
See A035491 for (the relevant part of) the deck after the n-th step. - M. F. Hasler, Aug 13 2022
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REFERENCES
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D. Gale, Mathematical Entertainments: "Careful Card-Shuffling and Cutting Can Create Chaos," The Mathematical Intelligencer, vol. 14, no. 1, 1992, pages 54-56.
D. Gale, Tracking the Automatic Ant and Other Mathematical Explorations, A Collection of Mathematical Entertainments Columns from The Mathematical Intelligencer, Springer, 1998.
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LINKS
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FORMULA
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a(n) = A035491(n,1), i.e., the first element of the n-th row of that table, for all n > 0. - M. F. Hasler, Aug 13 2022
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PROG
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(Python)
def aupton(terms):
alst, deck = [1], list(range(1, 2*terms+1))
for n in range(1, terms+1):
first, next = deck[:n], deck[n:2*n]
deck[0:2*n:2] = next
deck[1:2*n:2] = first
alst.append(deck[0])
return alst
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CROSSREFS
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KEYWORD
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nonn,easy,nice
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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