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A295691
a(n) = a(n-1) + a(n-3) + a(n-4), where a(0) = 2, a(1) = 2, a(2) = 2, a(3) = 1.
1
2, 2, 2, 1, 5, 9, 12, 18, 32, 53, 83, 133, 218, 354, 570, 921, 1493, 2417, 3908, 6322, 10232, 16557, 26787, 43341, 70130, 113474, 183602, 297073, 480677, 777753, 1258428, 2036178, 3294608, 5330789, 8625395, 13956181, 22581578, 36537762, 59119338, 95657097
OFFSET
0,1
COMMENTS
a(n)/a(n-1) -> (1 + sqrt(5))/2 = golden ratio (A001622), so that a( ) has the growth rate of the Fibonacci numbers (A000045).
FORMULA
a(n) = a(n-1) + a(n-3) + a(n-4), where a(0) = 2, a(1) = 2, a(2) = 2, a(3) = 1.
G.f.: (-2 + 3 x^3)/(-1 + x + x^3 + x^4).
MATHEMATICA
LinearRecurrence[{1, 0, 1, 1}, {2, 2, 2, 1}, 100]
CROSSREFS
Sequence in context: A307739 A109978 A114293 * A285183 A255399 A181830
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Nov 29 2017
STATUS
approved