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A026519 Triangular array T read by rows: T(i,0)=T(i,2i)=1 for i >= 0, T(i,1)=T(i,2i-1)=[ (i+1)/2 ] for i >= 1; for even n >= 2, T(i,j)=T(i-1,j-2)+T(i-1,j) for 2<=j<=2i-2; for odd n >= 3, T(i,j)=T(i-1,j-2)+T(i-1,j-1)+T(i-1,j) for 2<=j<=2i-2. 20
1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 2, 4, 4, 4, 2, 1, 1, 2, 5, 6, 8, 6, 5, 2, 1, 1, 3, 8, 13, 19, 20, 19, 13, 8, 3, 1, 1, 3, 9, 16, 27, 33, 38, 33, 27, 16, 9, 3, 1, 1, 4, 13, 28, 52, 76, 98, 104, 98, 76, 52, 28, 13, 4, 1, 1, 4, 14, 32, 65, 104, 150, 180, 196, 180 (list; table; graph; refs; listen; history; internal format)
OFFSET

1,7

FORMULA

T(n, k) = number of integer strings s(0), ..., s(n) such that s(0)=0, s(n)=n-k, |s(i)-s(i-1)|=1 if i is even, |s(i)-s(i-1)|<= 1 if i is odd.

CROSSREFS

Cf. A026527.

Sequence in context: A030424 A145515 A188919 * A025177 A026148 A117211

Adjacent sequences:  A026516 A026517 A026518 * A026520 A026521 A026522

KEYWORD

nonn,tabl

AUTHOR

Clark Kimberling (ck6(AT)evansville.edu)

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Last modified February 17 11:30 EST 2012. Contains 206011 sequences.