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A198892 E.g.f.: 1/[ Sum_{n>=0} (-x)^(n*(n+1)/2) / A000178(n) ] where A000178(n) = Product_{k=1..n} k!. 1
1, 1, 2, 9, 48, 300, 2280, 20580, 211680, 2434320, 31134600, 438807600, 6744276000, 112237725600, 2011760150400, 38639999197800, 791610365145600, 17230493212732800, 397111119429024000, 9660782144094681600, 247393077222459168000, 6651976858409613931200 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..21.

EXAMPLE

E.g.f.: A(x) = 1 + x + 2*x^2/2! + 9*x^3/3! + 48*x^4/4! + 300*x^5/5! +...

where

1/A(x) = 1 - x/1! - x^3/(1!*2!) + x^6/(1!*2!*3!) + x^10/(1!*2!*3!*4!) - x^15/(1!*2!*3!*4!*5!) - x^21/(1!*2!*3!*4!*5!*6!) ++--...

1/A(x) = 1 - x - x^3/2 + x^6/12 + x^10/288 - x^15/34560 - x^21/24883200 +...

PROG

(PARI) {a(n)=local(A=1/sum(m=0, sqrtint(2*n+1), (-x)^(m*(m+1)/2)/prod(k=1, m, k!)+x*O(x^n))); n!*polcoeff(A, n)}

CROSSREFS

Cf. A198891.

Sequence in context: A100427 A214404 A074143 * A205571 A052826 A246759

Adjacent sequences:  A198889 A198890 A198891 * A198893 A198894 A198895

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Oct 30 2011

STATUS

approved

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Last modified August 11 04:03 EDT 2020. Contains 336421 sequences. (Running on oeis4.)