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A026009 Triangular array T read by rows: T(n,0) = 1 for n >= 0; T(1,1) = 1; and for n >= 2, T(n,k) = T(n-1,k-1) + T(n-1,k) for k = 1,2,...,[(n+1)/2]; T(n,n/2 + 1) = T(n-1,n/2) if n is even. 18
1, 1, 1, 1, 2, 1, 1, 3, 3, 1, 4, 6, 3, 1, 5, 10, 9, 1, 6, 15, 19, 9, 1, 7, 21, 34, 28, 1, 8, 28, 55, 62, 28, 1, 9, 36, 83, 117, 90, 1, 10, 45, 119, 200, 207, 90, 1, 11, 55, 164, 319, 407, 297, 1, 12, 66, 219, 483, 726, 704, 297, 1, 13, 78, 285, 702, 1209, 1430, 1001, 1, 14, 91, 363, 987, 1911 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

LINKS

Table of n, a(n) for n=1..75.

FORMULA

T(n, k) = binomial(n, k) - binomial(n, k-3). - Darko Marinov (marinov(AT)lcs.mit.edu), May 17 2001

EXAMPLE

From Jonathon Kirkpatrick, Jul 01 2016: (Start)

Triangle begins:

1;

1,  1;

1,  2,  1;

1,  3,  3;

1,  4,  6,  3;

1,  5, 10,  9;

1,  6, 15, 19,    9;

1,  7, 21, 34,   28;

1,  8, 28, 55,   62,   28;

1,  9, 36, 83,  117,   90;

1, 10, 45, 119, 200,  207,   90;

1, 11, 55, 164, 319,  407,  297;

1, 12, 66, 219, 483,  726,  704,  297;

1, 13, 78, 285, 702, 1209, 1430, 1001;

... (End)

CROSSREFS

Cf. A026016, A000217.

Sequence in context: A299208 A334187 A082870 * A137171 A010356 A100640

Adjacent sequences:  A026006 A026007 A026008 * A026010 A026011 A026012

KEYWORD

nonn,tabf,easy

AUTHOR

Clark Kimberling

STATUS

approved

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Last modified July 11 08:10 EDT 2020. Contains 335626 sequences. (Running on oeis4.)