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A025177 Triangular array, read by rows: first differences in n,n direction of trinomial array A027907. 23
1, 1, 0, 1, 1, 1, 2, 1, 1, 1, 2, 4, 4, 4, 2, 1, 1, 3, 7, 10, 12, 10, 7, 3, 1, 1, 4, 11, 20, 29, 32, 29, 20, 11, 4, 1, 1, 5, 16, 35, 60, 81, 90, 81, 60, 35, 16, 5, 1, 1, 6, 22, 56, 111, 176, 231, 252, 231, 176, 111, 56, 22, 6, 1, 1, 7, 29, 84, 189, 343, 518, 659, 714, 659, 518, 343 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,7

COMMENTS

The Motzkin transforms of the rows starting (1, 2), (1, 3) and (1, 4), extended by zeros after their last element, are apparently in A026134, A026109 and A026110. - R. J. Mathar, Dec 11 2008

LINKS

G. C. Greubel, Table of n, a(n) for the first 50 rows, flattened

FORMULA

T(n, k) = T(n-1, k-2) + T(n-1, k-1) + T(n-1, k), starting with [1], [1, 0, 1].

G.f.: (1-yz)/[1-z(1+y+y^2)].

EXAMPLE

               1

            1  0  1

         1  1  2  1  1

      1  2  4  4  4  2  1

   1  3  7 10 12 10  7  3  1

1  4 11 20 29 32 29 20 11  4  1

MAPLE

A025177 := proc(n, k)

    option remember;

    if k < 0 or k > 2*n then

        0;

    elif n = 0 then

        1 ;

    elif n = 1 then

        op(k+1, [1, 0, 1]) ;

    else

        procname(n-1, k-2)+procname(n-1, k-1)+procname(n-1, k) ;

    end if;

end proc:

seq(seq(A025177(n, k), k=0..2*n), n=0..20)  ; # R. J. Mathar, Feb 25 2015

MATHEMATICA

CoefficientList[CoefficientList[Series[(1 - y*x)/(1 - x*(1 + y + y^2)), {x, 0, 10}, {y, 0, 10}], x], y] // Flatten (* G. C. Greubel, May 22 2017 *)

PROG

(PARI) {T(n, k) = if( k<0 || k>2*n, 0, if( n==0, 1, if( n==1, [1, 0, 1][k+1], if( n==2, [1, 1, 2, 1, 1][k+1], T(n-1, k-2) + T(n-1, k-1) + T(n-1, k)))))};

(PARI) T(n, k)=polcoeff(Ser(polcoeff(Ser((1-y*z)/(1-z*(1+y+y^2)), y), k, y), z), n, z)

(PARI) {T(n, k) = if( k<0 || k>2*n, 0, if( n==0, 1, polcoeff( (1 + x + x^2)^n, k) - polcoeff( (1 + x + x^2)^(n-1), k-1)))};

(PARI) g=matrix(33, 65);

for(n=0, 32, for(k=0, 2*n, g[n+1, k+1]=0));

g[1, 1]=1;

g[2, 1]=1; g[2, 2]=0; g[2, 3]=1;

g[3, 1]=1; g[3, 2]=1; g[3, 3]=2; g[3, 4]=1; g[3, 5]=1;

for(n=0, 2, for(k=0, 2*n, print(n, " ", k, " ", g[n+1, k+1])))

for(n=3, 32, g[n+1, 1]=1; print(n, " 1 1"); g[n+1, 2]=n-1; print(n, " 2 ", n-1); for(k=2, 2*n, g[n+1, k+1]=g[n, k-1]+g[n, k]+g[n, k+1]; print(n, " ", k, " ", g[n+1, k+1])))

\\ Michael B. Porter, Feb 02 2010

CROSSREFS

Columns include A025178, A025179, A025180, A025181, A025182.

Cf. A024996.

Sequence in context: A272896 A188919 A026519 * A026148 A117211 A246576

Adjacent sequences:  A025174 A025175 A025176 * A025178 A025179 A025180

KEYWORD

nonn,tabf,easy

AUTHOR

Clark Kimberling

EXTENSIONS

Edited by Ralf Stephan, Jan 09 2005

Offset corrected by R. J. Mathar, Feb 25 2015

STATUS

approved

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Last modified October 20 05:16 EDT 2018. Contains 316378 sequences. (Running on oeis4.)