**a(n) = p^n + q^n, where p = (3 + sqrt 21)/2, q = (3 - sqrt 21)/2.**

*3, 15, 54, 207, 783, 2970, 11259, 42687, 161838, 613575, 2326239, 8819442*

*1 seqfan posts*

Index of A-numbers in seqfan: by ascending order by month by frequency by keyword

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