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a(n) = (3*(1 + (-1)^n)*2^(n/2) - (2 - 2^n)*(1 - (-1)^n)*(2 - 2^n))/12. - Colin Barker, Mar 26 2019
Table[(3 (1 + (-1)^n) 2^(n/2) - (2 - 2^n) (1 - (-1)^n) (2 - 2^n))/12, {n, 3, 50}] (* Bruno Berselli, Mar 26 2019 *)
a(n) = (-2 + 2*(-1)^n + 3*2^(n/2) 1 + 3*(-1)^n)*2^(n/2) + - (2 - 2^n )*(1 - (-1)^n*2^n) )/ 12. - Colin Barker, Mar 26 2019
Table[(3 (1 + (-1)^n) 2^(n/2) - (2 - 2^n) (1 - (-1)^n))/12, {n, 3, 50}] (* Bruno Berselli, Mar 26 2019 *)
a(n) = (-2 + 2*(-1)^n + 3*2^(n/2) + 3*(-1)^n*2^(n/2) + 2^n + - (-1)^(1+n)*2^n) / 12. - Colin Barker, Mar 26 2019
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a(n) = (2^n - 2)/6 if n is odd else 3*2^(n/2 - 1)/6. - Peter Luschny, Mar 26 2019
def a(n): return ((2^n - 2) //6 if is_odd(n) else 3*2^(n//2-1)) // 6
a(n) = (2^n - 2)/6 if n is odd else 3*2^(n/2)/6. - Peter Luschny, Mar 26 2019
(Sage)
def a(n): return ((2^n - 2) if is_odd(n) else 3*2^(n//2)) // 6
print([a(n) for n in (3..41)]) # Peter Luschny, Mar 26 2019
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a(n) = 7*a(n-2) - 14*a(n-4) + 8*a(n-6) for n > 58. - Chai Wah Wu, Jun 19 2016
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