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 A199540 Expansion 1/(1-x^2*cotan(x))=sum(n>=0, a(n)*x^n/(n)!^2. 0
 1, 1, 4, 24, 192, -320, -138240, -10214400, -669204480, -43782488064, -2628064051200, -91419903590400, 14288196206592000, 5367226212019077120, 1259862249808204922880, 257126813359346810880000, 46529454048255997378560000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS FORMULA a(n) = n!^2*sum(m=1..n, (2^(n-2*m)*(-1)^((n-m)/2)*sum(l=0..m, (2^l*l! *C(m,l)* sum(k=0..n-2*m+l, (k!*stirling1(l+k,l)*stirling2(n-2*m+l,k))/ ((l+k)!*(n-2*m+l)!)))))), a(0)=1. PROG (Maxima) a(n):=if n=0 then 1 else n!^2*sum((2^(n-2*m)*(-1)^((n-m)/2) *sum((2^l*l! *binomial(m, l)* sum((k!*stirling1(l+k, l)*stirling2(n-2 *m+l, k))/((l+k)!*(n-2*m+l)!), k, 0, n-2*m+l)), l, 0, m)), m, 1, n); CROSSREFS Sequence in context: A001506 A088815 A193854 * A036691 A002866 A182798 Adjacent sequences:  A199537 A199538 A199539 * A199541 A199542 A199543 KEYWORD sign AUTHOR Vladimir Kruchinin, Nov 07 2011 STATUS approved

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