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 A273461 Number of physically stable n X n placements of water source-blocks in Minecraft. 4
 1, 2, 9, 40, 484, 9717, 338724, 21624680, 2504301849, 520443847520, 195145309791364, 131850659243316222, 160668896658179472676, 352891729183598844656996, 1397187513066371784602204416, 9972288382286063615850619475640 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS In Minecraft worlds, a source block of water can be reacted with another source block, two blocks away. This reaction creates a third "infinite" source block in the unoccupied intermediate block, so called because if the intermediate water source is destroyed or picked up by a player using a bucket, it will immediately regenerate itself. A placement of water at several positions in an n X n board is said to be *stable* if no infinite water physics can in fact occur (under otherwise optimal conditions). This means that the total quantity of water in the system is held constant. In short, no two source blocks can be graph-distance 2 from each other. - Gus Wiseman, Nov 27 2019 Often incorrectly described as cellular automata, the observed behaviors of liquids within a board are inseparable in certain ways from states of affair outside of the board and events outside of the system. This aspect of Minecraft is poorly understood. LINKS EthosLab, Minecraft - Tutorial: Water Wikipedia, Distance (graph theory) Christopher Cormier, C# Program EXAMPLE a(2) = 9: {{}, {(2,2)}, {(2,1)}, {(2,1),(2,2)}, {(1,2)}, {(1,2),(2,2)}, {(1,1)}, {(1,1),(2,1)}, {(1,1),(1,2)}}. MATHEMATICA stableSets[u_, Q_]:=If[Length[u]===0, {{}}, With[{w=First[u]}, Join[stableSets[DeleteCases[u, w], Q], Prepend[#, w]&/@stableSets[DeleteCases[u, r_/; r===w||Q[r, w]||Q[w, r]], Q]]]]; allflows[n_]:=stableSets[Join@@Array[List, {n, n}], Function[{v, w}, Plus@@Abs/@(w-v)===2]]; Table[Length[allflows[i]], {i, 6}] (* Gus Wiseman, May 23 2016 *) CROSSREFS The one-dimensional version is A006498. Dominated by A329871. Cf. A002416, A005251, A027624, A114901. Sequence in context: A259339 A052322 A130767 * A217190 A020698 A128752 Adjacent sequences:  A273458 A273459 A273460 * A273462 A273463 A273464 KEYWORD nonn AUTHOR Gus Wiseman, May 23 2016 EXTENSIONS a(7) from Tae Lim Kook, May 25 2016 a(8) from Tae Lim Kook, May 29 2016 a(7)-a(8) corrected by Christopher Cormier, Dec 17 2019 a(9)-a(15) from Christopher Cormier, Dec 19 2019 STATUS approved

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Last modified August 7 08:55 EDT 2020. Contains 336274 sequences. (Running on oeis4.)