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A101473
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Boustrophedon transform of the Jacobsthal numbers.
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2
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0, 1, 3, 9, 31, 111, 453, 2059, 10571, 60651, 386253, 2704659, 20661411, 170990691, 1523975053, 14552848059, 148234015051, 1604267622731, 18383552327853, 222363321668259, 2831217743661491, 37850593064646771, 530121590756400653
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OFFSET
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0,3
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COMMENTS
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LINKS
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FORMULA
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E.g.f.: (sec(x) + tan(x))*(exp(2*x) - exp(-x))/3.
a(n) ~ n! * 2^(n+2) * (exp(Pi) - exp(-Pi/2)) / (3 * Pi^(n+1)). - Vaclav Kotesovec, Jun 12 2015
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PROG
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(Python)
from itertools import accumulate, islice
def A101473_gen(): # generator of terms
blist, a, b = tuple(), 0, 1
while True:
yield (blist := tuple(accumulate(reversed(blist), initial=a)))[-1]
a, b = b, 2*a+b
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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