A099139 - OEIS

A099139

a(n) = (18^n - (-6)^n)/24.

0, 1, 12, 252, 4320, 79056, 1415232, 25520832, 459095040, 8265390336, 148766948352, 2677865536512, 48201216860160, 867624080265216, 15617220384079872, 281110045277601792, 5059980344811847680, 91079649027723165696, 1639433665572357537792, 29509806081862392348672

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OFFSET

0,3

COMMENTS

In general k^(n-1)*A015518(n) is given by ((3k)^n-(-k)^n)/(4k) with g.f. x/((1+kx)(1-3kx)).

LINKS

Table of n, a(n) for n=0..19.

Index entries for linear recurrences with constant coefficients, signature (12,108).

FORMULA

G.f.: x/((1+6x)*(1-18x)).

a(n) = 12a(n-1)+108a(n-2). a(n) = 6^(n-1)*A015518(n).

MATHEMATICA