cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A227764 Losing positions in the misere version of the Subtract-a-Prime game.

Original entry on oeis.org

2, 3, 11, 12, 27, 36, 37, 51, 57, 87, 93, 102, 117, 123, 127, 135, 147, 157, 171, 177, 189, 197, 207, 219, 237, 249, 255, 261, 267, 291, 297, 303, 311, 312, 321, 327, 337, 345, 357, 363, 377, 387, 393, 397, 405, 417, 427, 447, 453, 471, 477, 483, 487, 495
Offset: 1

Views

Author

José María Grau Ribas, Jul 29 2013

Keywords

Comments

Consider the following game: two players make moves in turn; initially the number on the board is n. Each move consists of subtracting a prime number that is at most the number on the board. The player who cannot play wins. This sequence is the set of lost positions in this game.

Crossrefs

Cf. A227691, A025043, A227763.

Programs

  • Mathematica
    moves[n_] := Table[n - Prime[i], {i, 1, PrimePi[n]}]; gana[n_] := gana[n] = If[n < 2, True, ! Select[moves[n], !gana[#] &] == {}]; Select[Range[155], !gana[#] &]

A340780 Losing positions n (P-positions) in the following game: two players take turns dividing the current value of n by either a prime power > 1 or by A007947(n) to obtain the new value of n. The winner is the player whose division results in 1.

Original entry on oeis.org

1, 12, 18, 20, 28, 44, 45, 50, 52, 63, 68, 75, 76, 92, 98, 99, 116, 117, 120, 124, 147, 148, 153, 164, 168, 171, 172, 175, 188, 207, 212, 216, 236, 242, 244, 245, 261, 264, 268, 270, 275, 279, 280, 284, 292, 312, 316, 325, 332, 333, 338, 356, 363, 369, 378, 387, 388
Offset: 1

Views

Author

José María Grau Ribas, Jan 21 2021

Keywords

Comments

The game is equivalent to the game of Nim with the additional allowed move consisting of removing one object from each pile.

Crossrefs

Cf. A003557, A227691, A227763, A227764, A171947, A005240, A081691, A099352, A171945, A171949, A285304, A120442, A137295, A275432.

Programs

  • Mathematica
    Clear[moves,los]; A003557[n_]:= {Module[{aux = FactorInteger[n], L=Length[FactorInteger[n]]},Product[aux[[i,1]]^(aux[[i, 2]]-1),{i, L}]]};
moves[n_] :=moves[n] = Module[{aux = FactorInteger[n], L=Length[ FactorInteger [n]]}, Union[Flatten[Table[n/aux[[i,1]]^j, {i,1,L},{j,1,aux[[i,2]]}],1], A003557[n]]]; los[1]=True; los[m_] := los[m] = If[PrimeQ[m], False, Union@Flatten@Table[los[moves[m][[i]]], {i,1,Length[moves[m]]}] == {False}]; Select[Range[400], los]
Showing 1-2 of 2 results.

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