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A236420

Riordan array (1/(1-3*x), (1-3*x-sqrt(1-6*x+5*x^2))/(2*x)).

1, 3, 1, 9, 6, 1, 27, 28, 9, 1, 81, 120, 56, 12, 1, 243, 497, 300, 93, 15, 1, 729, 2034, 1490, 594, 139, 18, 1, 2187, 8321, 7098, 3411, 1029, 194, 21, 1, 6561, 34248, 33026, 18360, 6692, 1632, 258, 24, 1, 19683, 142331, 151686, 94798, 40068, 11846, 2430, 331, 27, 1

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OFFSET

0,2

COMMENTS

T(n,0) = 3^n = A000244(n).

T(n,2) = A002212(n+1) - 3^n.

T(n+1,n) = 3n+3 = A008585(n+1).

T(n+2,n) = (9*n^2+29*n+18)/2.

LINKS

Table of n, a(n) for n=0..54.

FORMULA

T(n,0) = 3*T(n-1,0), T(n,k) = T(n-1,k-1) + 3*T(n-1,k) + T(n-1,k+1) for k>0, T(n,k) = 0 if k<0 or if k>n, T(0,0) = 1.