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A369490
a(n) = 3^(n+1) + 2*(-2)^(n+1).
2
-1, 17, 11, 113, 179, 857, 1931, 7073, 18659, 61097, 173051, 539633, 1577939, 4815737, 14283371, 43177793, 128878019, 387944777, 1161212891, 3488881553, 10456158899, 31389448217, 94126401611, 282463090913, 847221500579, 2542000046057
OFFSET
0,2
FORMULA
a(n) = a(n-1) + 6*a(n-2); a(0) = -1, a(1) = 17.
G.f.: (18*x-1)/((1+2*x)*(1-3*x)).
a(2*n) = A003063(2*n+2).
a(2*n+1) = A085279(2*n+3).
a(n) = 18*A015441(n) - A015441(n+1).
MATHEMATICA
LinearRecurrence[{1, 6}, {-1, 17}, 26] (* James C. McMahon, Jan 30 2024 *)
PROG
(Python)
def A369490(n): return 3**(n+1)+(1<<n+2 if n&1 else -(1<<n+2)) # Chai Wah Wu, Feb 25 2024
CROSSREFS
KEYWORD
sign,easy
AUTHOR
Philippe Deléham, Jan 24 2024
STATUS
approved