

A002900


Number of nstep 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[tg1, Append[p, e]], {e, mv}]]];
a[n_] := b[n]/2;
Table[an = a[n]; Print[an]; an, {n, 1, 16}] (* JeanFrançois 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

N. J. A. Sloane


EXTENSIONS

More terms from Hugo Pfoertner, Dec 23 2002


STATUS

approved



