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A122848
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Exponential Riordan array (1,x(1+x/2)).
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7
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1, 0, 1, 0, 1, 1, 0, 0, 3, 1, 0, 0, 3, 6, 1, 0, 0, 0, 15, 10, 1, 0, 0, 0, 15, 45, 15, 1, 0, 0, 0, 0, 105, 105, 21, 1, 0, 0, 0, 0, 105, 420, 210, 28, 1, 0, 0, 0, 0, 0, 945, 1260, 378, 36, 1, 0, 0, 0, 0, 0, 945, 4725, 3150, 630, 45, 1, 0, 0, 0, 0, 0, 0, 10395, 17325, 6930, 990, 55, 1, 0, 0
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OFFSET
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0,9
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COMMENTS
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Entries are Bessel polynomial coefficients. Row sums are A000085. Diagonal sums are A122849. Inverse is A122850. Product of A007318 and A122848 gives A100862.
T(n,k) is the number of self inverse permutations of {1,2,...,n} having exactly k cycles. -Geoffrey Critzer, May 8 2012.
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LINKS
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Table of n, a(n) for n=0..79.
T. Copeland, Infinitesimal Generators, the Pascal Pyramid, and the Witt and Virasoro Algebras
H. Han, S. Seo, Combinatorial proofs of inverse relations and log-concavity for Bessel numbers, Eur. J. Combinat. 29 (7) (2008) 1544-1554. [From R. J. Mathar, Mar 20 2009]
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FORMULA
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Number triangle T(n,k)=k!*C(n,k)/((2k-n)!*2^(n-k))
T(n,k)=A001498(k,n-k) - Michael Somos Oct 03 2006
E.g.f.: exp(y(x+x^2/2)) -Geoffrey Critzer, May 8 2012.
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EXAMPLE
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Triangle begins
1,
0, 1,
0, 1, 1,
0, 0, 3, 1,
0, 0, 3, 6, 1,
0, 0, 0, 15, 10, 1,
0, 0, 0, 15, 45, 15, 1,
0, 0, 0, 0, 105, 105, 21, 1
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MATHEMATICA
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t[n_, k_] := k!*Binomial[n, k]/((2 k - n)!*2^(n - k)); Table[ t[n, k], {n, 0, 11}, {k, 0, n}] // Flatten
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PROG
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(PARI) {T(n, k)=if(2*k<n|k>n, 0, n!/(2*k-n)!/(n-k)!*2^(k-n))} /* Michael Somos Oct 03 2006 */
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CROSSREFS
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Cf. A001497, A049403, A111924.
Sequence in context: A170846 A085604 A144357 * A054548 A059202 A144452
Adjacent sequences: A122845 A122846 A122847 * A122849 A122850 A122851
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KEYWORD
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easy,nonn,tabl
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AUTHOR
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Paul Barry, Sep 14 2006
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STATUS
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approved
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