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A182316
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a(n) = binomial(n^2 + 3*n, n) / (n+1)^2.
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3
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1, 1, 5, 51, 819, 18278, 527085, 18730855, 793542167, 39113958819, 2201663313200, 139461523272085, 9824294829146550, 762188806010669820, 64595315110014533629, 5939055918736259991759, 588894813538193130767295, 62651281502108852275337225
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OFFSET
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0,3
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COMMENTS
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a(n) = < PF_n, PF_n >, where PF_n is the parking function symmetric function and <,> denotes the usual scalar product on symmetric functions (proved). - Richard Stanley, Sep 24 2015
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LINKS
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FORMULA
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a(n) = [x^n] 1/(1-x)^((n+1)^2) / (n+1)^2 ; that is, a(n) equals the coefficient of x^n in 1/(1-x)^((n+1)^2) divided by (n+1)^2.
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MAPLE
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PROG
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(PARI) {a(n)=binomial((n+1)^2+n-1, n)/(n+1)^2}
for(n=0, 20, print1(a(n), ", "))
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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