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 A001464 E.g.f. exp( -x -(1/2)*x^2 ). (Formerly M0361 N0137) 13
 1, -1, 0, 2, -2, -6, 16, 20, -132, -28, 1216, -936, -12440, 23672, 138048, -469456, -1601264, 9112560, 18108928, -182135008, -161934624, 3804634784, -404007680, -83297957568, 92590134208, 1906560847424, -4221314202624, -45349267830400, 159324751301248 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 COMMENTS Signed row sums of Hermite polynomials p(k, x) = x*p(k - 1, x) - (n - 1)*p(k - 2, x). - Roger L. Bagula, Oct 06 2006 From Robert Israel, Apr 27 2017: (Start) (-1)^n*a(n) is (the number of even involutions) - (the number of odd involutions) in the symmetric group S_n. a(n) == (-1)^n (mod A069834(n-1)) for n >= 3. a(n) is divisible by n-2 and by A200675(n+2). (End) REFERENCES Eugene Jahnke and Fritz Emde, Table of Functions with Formulae and Curves, Dover Publications, New York, 1945, page 32 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Robert Israel, Table of n, a(n) for n = 0..807 John Campbell, A class of symmetric difference-closed sets related to commuting involutions, Discrete Mathematics & Theoretical Computer Science, Vol 19 no. 1, 2017. R. Israel, Solution to Problem 91-9: Even Minus Odd Involutions in the Symmetric Group, SIAM Review 34(2)(1992),315-317. L. Moser and M. Wyman, On solutions of x^d = 1 in symmetric groups, Canad. J. Math., 7 (1955), 159-168. FORMULA a(n) = -h(n, -1) where h(n, x) is the Hermite polynomial h(n, x)=sum(k=0, floor(n/2), (-1)^k*binomial(n, 2*k)*prod(i=0, k, 2*i-1)*x^(n-2*k)). - Benoit Cloitre, May 01 2003 a(n) = (-1)^n*sum(k=0, floor(n/2), (-1)^k*C(n, 2*k)*(2k-1)!!). - Benoit Cloitre, May 01 2003 a(0)=1, a(1)=-1; a(n)=-a(n-1)-(n-1)*a(n-2). - Matthew J. White (mattjameswhite(AT)hotmail.com), Mar 01 2006 From Sergei N. Gladkovskii, Oct 12 2012, Nov 04 2012, Apr 17 2013, Nov 13 2013: (Start) Continued fractions: G.f.: 1/(U(0) + x) where U(k) = 1 + x*(k+1) - x*(k+1)/(1 + x/U(k+1)). G.f.: 1/U(0) where U(k) = 1 + x + x^2*(k+1)/U(k+1). G.f.: 1/Q(0) where Q(k) = 1 + x*k + x/(1 - x*(k+1)/Q(k+1)). G.f.: T(0)/(1+x) where T(k) = 1 - x^2*(k+1)/(x^2*(k+1) + (1+x)^2/T(k+1)). (End) Binomial transform is [1,0,-1,0,3,0,-15,0,105,...] where A001147 = [1,1,3,15,105,...]. - Michael Somos, Jan 24 2014 Hankel transform is [1,-1,-2,12,288,-34560,-24883200,...] where A000178 = [1,1,2,12,288,34560,24883200,...]. - Michael Somos, Jan 24 2014 0 = a(n) * (-a(n+1) - a(n+2) - a(n+3)) + a(n+1) * (a(n+1) + a(n+2)) for all n in Z. - Michael Somos, Jan 24 2014 a(n) = -(-1)^n*y(n,n), where y(m+1,n) = y(m,n) - (n-m)*y(m-1,n), with y(0,n)=0, y(1,n)=y(2,n)=1 for all n. - Benedict W. J. Irwin, Nov 03 2016 a(n) = (-1)^n*2^((n-1)/2)*KummerU((1-n)/2, 3/2, 1/2). - Peter Luschny, Apr 30 2017 EXAMPLE G.f. = 1 - x + 2*x^3 - 2*x^4 - 6*x^5 + 16*x^6 + 20*x^7 - 132*x^8 + ... MAPLE f:= gfun:-rectoproc({a(n)=-a(n-1)-(n-1)*a(n-2), a(0)=1, a(1)=-1}, a(n), remember): map(f, [\$0..100]); # Robert Israel, Apr 27 2017 a := n -> (-1)^n*2^((n-1)/2)*KummerU((1-n)/2, 3/2, 1/2): seq(simplify(a(n)), n=0..28); # Peter Luschny, Apr 30 2017 MATHEMATICA p[0, x] = 1; p[1, x] = x; p[k_, x_] := p[k, x] = x*p[k - 1, x] - (n - 1)*p[k - 2, x]; Table[Expand[p[n, x]], {n, 0, 10}]; Table[Sum[CoefficientList[p[n, x], x][[m]], {m, 1, Length[CoefficientList[p[ n, x], x]]}], {n, 0, 15}]; (* Roger L. Bagula, Oct 06 2006 *) With[{nn=30}, CoefficientList[Series[Exp[-x-1/2 x^2], {x, 0, nn}], x]Range[0, nn]!] (* Harvey P. Dale, Sep 16 2011 *) a[ n_] := If[ n < 0, 0, HermiteH[ n, Sqrt[1/2]] (-Sqrt[1/2])^n]; (* Michael Somos, Jan 24 2014 *) a[ n_] := If[ n < 0, 0, (-1)^n Sum[ (-1)^k Binomial[ n, 2 k] (2 k - 1)!!, {k, 0, n/2}]]; (* Michael Somos, Jan 24 2014 *) Table[(-1)^(n + 1)*DifferenceRoot[Function[{y, m}, {y[1 + m] == y[m] - (n - m) y[m - 1], y[0] == 0, y[1] == 1, y[2] == 1}]][n], {n, 1, 30}] (* Benedict W. J. Irwin, Nov 03 2016 *) PROG (PARI) Vec( serlaplace( exp( -x -(1/2)*x^2 + O(x^66) ) ) ) /* Joerg Arndt, Oct 13 2012 */ (PARI) {a(n) = if( n<0, 0, (-1)^n * sum(k=0, n\2, (-1/2)^k * n! / (k! * (n - 2*k)!)))}; /* Michael Somos, Jan 24 2014 */ CROSSREFS Cf. A099174, A000085, A066325. Cf. A001147, A000178, A069834, A200675. Sequence in context: A083555 A303150 A233147 * A067136 A180068 A034439 Adjacent sequences:  A001461 A001462 A001463 * A001465 A001466 A001467 KEYWORD sign,easy AUTHOR EXTENSIONS 13th and 14th terms corrected by Simon Plouffe STATUS approved

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Last modified October 17 21:37 EDT 2019. Contains 328134 sequences. (Running on oeis4.)