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A108351 Diagonal sums of symmetric triangle A108350. 1
1, 1, 2, 3, 5, 8, 14, 24, 43, 77, 140, 255, 467, 856, 1572, 2888, 5309, 9761, 17950, 33011, 60713, 111664, 205378, 377744, 694775, 1277885, 2350392, 4323039, 7951303, 14624720, 26899048, 49475056, 90998809, 167372897, 307846746 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..34.

Index entries for linear recurrences with constant coefficients, signature (2,1,-2,-1,0,1).

FORMULA

G.f.: (1-x-x^2)/((1+x)(1-x)^2(1-x-x^2-x^3)); a(n)=2a(n-1)+a(n-2)-2a(n-3)-a(n-4)+a(n-6); a(n)=sum{k-0..floor(n/2), sum{j=0..n-2k, C(k, j)C(n-k-j, k)*(1+(-1)^j)/2}}.

MATHEMATICA

LinearRecurrence[{2, 1, -2, -1, 0, 1}, {1, 1, 2, 3, 5, 8}, 40] (* Harvey P. Dale, Nov 24 2017 *)

CROSSREFS

Sequence in context: A274110 A260403 A127603 * A038495 A007059 A079500

Adjacent sequences:  A108348 A108349 A108350 * A108352 A108353 A108354

KEYWORD

easy,nonn

AUTHOR

Paul Barry, May 31 2005

STATUS

approved

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Last modified February 19 21:14 EST 2019. Contains 320328 sequences. (Running on oeis4.)