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A349088 a(n) = n! * Sum_{k=0..floor((n-1)/3)} 1 / (3*k+1)!. 1
0, 1, 2, 6, 25, 125, 750, 5251, 42008, 378072, 3780721, 41587931, 499055172, 6487717237, 90828041318, 1362420619770, 21798729916321, 370578408577457, 6670411354394226, 126737815733490295, 2534756314669805900, 53229882608065923900, 1171057417377450325801 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,3
LINKS
FORMULA
E.g.f.: (exp(x) - 2 * exp(-x/2) * sin((Pi - 3*sqrt(3)*x)/6)) / (3*(1 - x)).
a(n) = floor(c * n!) for n > 0, where c = 1.041865355... = A143820.
MATHEMATICA
Table[n! Sum[1/(3 k + 1)!, {k, 0, Floor[(n - 1)/3]}], {n, 0, 22}]
nmax = 22; CoefficientList[Series[(Exp[x] - 2 Exp[-x/2] Sin[(Pi - 3 Sqrt[3] x)/6])/(3 (1 - x)), {x, 0, nmax}], x] Range[0, nmax]!
CROSSREFS
Sequence in context: A370511 A074010 A352660 * A030806 A030828 A030839
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Mar 25 2022
STATUS
approved

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Last modified May 25 15:42 EDT 2024. Contains 372800 sequences. (Running on oeis4.)