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A198891 E.g.f.: 1/[ Sum_{n>=0} (-x)^(n*(n+1)/2) / (n*(n+1)/2)! ]. 2
1, 1, 2, 7, 32, 180, 1219, 9646, 87192, 886536, 10016159, 124481258, 1687686528, 24787991800, 392081193504, 6644677619581, 120115898158288, 2307044712629472, 46917527736860976, 1007152702625923440, 22757886107313170356, 539955309450787483261, 13421068671117864869156 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..22.

EXAMPLE

E.g.f.: A(x) = 1 + x + 2*x^2/2! + 7*x^3/3! + 32*x^4/4! + 180*x^5/5! +...

where

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

1/A(x) = 1 - x - x^3/6 + x^6/720 + x^10/3628800 - x^15/1307674368000 +...

PROG

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

CROSSREFS

Cf. A198892.

Sequence in context: A265165 A301465 A097900 * A000153 A006154 A000987

Adjacent sequences:  A198888 A198889 A198890 * A198892 A198893 A198894

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Oct 30 2011

STATUS

approved

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Last modified October 16 21:10 EDT 2019. Contains 328103 sequences. (Running on oeis4.)