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A003128
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Number of driving-point impedances of an n-terminal network.
(Formerly M4210)
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13
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0, 0, 1, 6, 31, 160, 856, 4802, 28337, 175896, 1146931, 7841108, 56089804, 418952508, 3261082917, 26403700954, 221981169447, 1934688328192, 17454004213180, 162765041827846, 1566915224106221, 15553364227949564, 159004783733999787, 1672432865100333916
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OFFSET
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0,4
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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FORMULA
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a(n) = (Bell(n) - 3*Bell(n+1) + Bell(n+2))/2. - Vladeta Jovovic, Aug 07 2006
a(n) = Sum_{k=1..n} binomial(k,2)*Stirling2(n,k), Stirling transform of A000217.
a(n) = (1/(2*exp(1)))*Sum_{k>=0} k^n*(k^2-3*k+1)/k!. Note that k^2-3*k+1 = k*(k-1)-2*k+1 is an example of a Poisson-Charlier polynomial.
a(n) = D^n(x^2/2!*exp(x)) evaluated at x = 0, where D is the operator (1+x)*d/dx. Cf. A005493.
E.g.f.: (1/2)*exp(exp(x)-1)*(exp(x)-1)^2 = x^2/2! + 6*x^3/3! + 31*x^4/4! + ...
O.g.f.: Sum_{k>=0} binomial(k,2)*x^k/Product_{i=1..k} (1-i*x) = x^2 + 6*x^3 + 31*x^4 + ... (End)
a(n) ~ n^2 * Bell(n) / (2*LambertW(n)^2) * (1 - 3*LambertW(n)/n). - Vaclav Kotesovec, Jul 28 2021
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MAPLE
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MATHEMATICA
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max = 23; CoefficientList[ Series[1/2*(E^x - 1)^2*E^(E^x - 1), {x, 0, max}], x]*Range[0, max]! (* Jean-François Alcover, Oct 04 2013, after e.g.f. *)
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PROG
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(Maxima) makelist((belln(n)-3*belln(n+1)+belln(n+2))/2, n, 0, 12); /* Emanuele Munarini, Jul 14 2011 */
(Haskell)
a003128 n = a003128_list !! n
a003128_list = zipWith3 (\x y z -> (x - 3 * y + z) `div` 2)
a000110_list (tail a000110_list) (drop 2 a000110_list)
(Python)
# Python 3.2 or higher required
from itertools import accumulate
A003128_list, blist, a, b = [], [1], 1, 1
for _ in range(30):
....blist = list(accumulate([b]+blist))
....c = blist[-1]
....A003128_list.append((c+a-3*b)//2)
(Magma) [(Bell(n) - 3*Bell(n+1) + Bell(n+2))/2: n in [0..30]]; // Vincenzo Librandi, Sep 19 2014
(SageMath)
def A003128(n): return (bell_number(n) - 3*bell_number(n+1) + bell_number(n+2))/2
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CROSSREFS
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KEYWORD
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nonn,nice
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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