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A052174
Triangle of numbers arising in enumeration of walks on square lattice.
0
1, 1, 1, 3, 2, 1, 6, 8, 3, 1, 20, 20, 15, 4, 1, 50, 75, 45, 24, 5, 1, 175, 210, 189, 84, 35, 6, 1, 490, 784, 588, 392, 140, 48, 7, 1, 1764, 2352, 2352, 1344, 720, 216, 63, 8, 1, 5292, 8820, 7560, 5760, 2700, 1215, 315, 80, 9, 1
OFFSET
0,4
LINKS
R. K. Guy, Catwalks, sandsteps and Pascal pyramids, J. Integer Sequences, Vol. 3 (2000), Article #00.1.6.
FORMULA
T(n, y) equals C(n+1,k)*C(n,k) - C(n+1,k)*C(n,k-1) if n-y = 2k, else if n-y = 2k+1 equals C(n+1,k)*C(n,k+1) - C(n+1,k+1)*C(n,k-1) (using article notation). - Michel Marcus, Oct 12 2014
EXAMPLE
First few rows:
1;
1 1;
3 2 1;
6 8 3 1;
20 20 15 4 1;
50 75 45 24 5 1;
175 210 189 84 35 6 1;
...
MATHEMATICA
c = Binomial; T[n_, m_] /; EvenQ[n-m] := (k = (n-m)/2; c[n+1, k]*c[n, k] - c[n+1, k]*c[n, k-1]); T[n_, m_] /; OddQ[n-m] := (k = (n-m-1)/2; c[n+1, k]*c[n, k+1] - c[n+1, k+1]*c[n, k-1]); Table[T[n, m], {n, 0, 9}, {m, 0, n}] // Flatten (* Jean-François Alcover, Jan 13 2015, after Michel Marcus *)
PROG
(PARI) tabl(nn) = {alias(C, binomial); for (n=0, nn, for (k=0, n, if (!((n-k) % 2), kk = (n-k)/2; tnk = C(n+1, kk)*C(n, kk) - C(n+1, kk)*C(n, kk-1), kk = (n-k-1)/2; tnk = C(n+1, kk)*C(n, kk+1) - C(n+1, kk+1)*C(n, kk-1)); print1(tnk, ", "); ); print(); ); } \\ Michel Marcus, Oct 12 2014
CROSSREFS
Cf. A005558 (first column), A005559, A005560, A005561, A005562.
Sequence in context: A202390 A210858 A114586 * A227790 A181897 A337977
KEYWORD
nonn,tabl,easy,nice
AUTHOR
N. J. A. Sloane, Jan 26 2000
STATUS
approved