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 A002900 Number of n-step walks on square lattice. (Formerly M1621 N0634) 3
 2, 6, 18, 50, 142, 390, 1086, 2958, 8134, 22050, 60146, 162466, 440750, 1187222, 3208298, 8622666, 23233338, 62329366, 167558310, 448848582, 1204403014, 3222280242, 8633306906, 23073198658, 61740677454, 164856393110, 440658745814 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Hugo Pfoertner, Table of n, a(n) for n = 1..79 FORMULA a(n) = (1/2) * A001411(n). MATHEMATICA (* b = A001411 *) mo = Tuples[{-1, 1}, 2]; b[0] = 1; b[tg_, p_:{{0, 0}}] := b[tg, p] = Block[{e, mv = Complement[Last[p] + #& /@ mo, p]}, If[tg == 1, Length[mv], Sum[b[tg-1, Append[p, e]], {e, mv}]]]; a[n_] := b[n]/2; Table[an = a[n]; Print[an]; an, {n, 1, 16}] (* Jean-François Alcover, Nov 02 2018, after Giovanni Resta in A001411 *) CROSSREFS A001411 is the main entry for this sequence. Cf. A046661. Sequence in context: A304962 A180282 A081154 * A309087 A199770 A204322 Adjacent sequences:  A002897 A002898 A002899 * A002901 A002902 A002903 KEYWORD nonn,walk AUTHOR EXTENSIONS More terms from Hugo Pfoertner, Dec 23 2002 STATUS approved

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Last modified December 5 19:53 EST 2020. Contains 338965 sequences. (Running on oeis4.)