Jacobsthal numbers
The Jacobsthal numbers are the numbers obtained by the Uns in the Lucas sequence with P=1 and Q=-2, corresponding to a = 2 and b = -1.
Jacobsthal numbers are defined by the recurrence relation:
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The first Jacobsthal numbers are:
0, 1, 1, 3, 5, 11, 21, 43, 85, 171, 341, 683, 1365, 2731, 5461, 10923, 21845, 43691, ……