OFFSET
0,2
COMMENTS
Boustrophedon transform of A001147.
LINKS
Robert Israel, Table of n, a(n) for n = 0..403
J. Millar, N. J. A. Sloane and N. E. Young, A new operation on sequences: the Boustrophedon transform, J. Combin. Theory, 17A (1996), 44-54 (Abstract, pdf, ps)
N. J. A. Sloane, Transforms
FORMULA
a(n) ~ (sec(1/2) + tan(1/2)) * 2^(n + 1/2) * n^n / exp(n). - Vaclav Kotesovec, Dec 21 2017
MAPLE
S:= series((sec(x)+tan(x))/sqrt(1-2*x), x, 51):
seq(coeff(S, x, n)*n!, n=0..50); # Robert Israel, Dec 21 2017
MATHEMATICA
nmax = 20; CoefficientList[Series[(Sec[x] + Tan[x])/Sqrt[1 - 2 x], {x, 0, nmax}], x] Range[0, nmax]!
PROG
(PARI) first(n) = x='x+O('x^n); Vec(serlaplace((1/cos(x) + tan(x))/sqrt(1-2*x))) \\ Iain Fox, Dec 21 2017
(Python)
from itertools import accumulate, count, islice
def A296792_gen(): # generator of terms
blist, m = tuple(), 1
for i in count(1, 2):
yield (blist := tuple(accumulate(reversed(blist), initial=m)))[-1]
m *= i
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Dec 20 2017
STATUS
approved