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FORMULA
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a(n) = 4*a(n-1) - 5*a(n-2) + 2*a(n-3).
a(n+1) = a(n-1) + 12*A000225(n). a(-1) = 3.
a(2*n) mod 9 = period 3: repeat [1, 4, 7].
a(2*n+1) mod 9 = 3.
a(n) mod 9 = period 6: repeat [1, 3, 4, 3, 7, 3].
a(n) mod 10 = period 20: repeat [1, 3, 3, 9, 7, 9, 9, 5, 3, 5, 5, 1, 9, 1, 1, 7, 5, 7, 7, 3] = Im(n). Im(n-1) = [3, 1, 3, 3, 9, 7, 9, 9, 5, 3, 5, 5, 1, 9, 1, 1, 7, 5, 7, 7]. Disordered [1, 1, 1, 1, 3, 3, 3, 3, 5, 5, 5, 5, 7, 7, 7, 7, 9, 9, 9, 9].
a(n+1) - a(n) = 2^(n+3) - 6.
G.f.: (1-x+6*x^2)/((1-2*x)*(1-x)^2).
E.g.f.: 8*exp(2*x) - (7 + 6*x)*exp(x). (End)
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