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A364176
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a(n) = (15*n)!*(5*n/2)!*(2*n)!/((15*n/2)!*(6*n)!*(5*n)!*n!).
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0
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1, 7168, 168043980, 4488240824320, 126694219977836700, 3688258943632086663168, 109504706026534324525391988, 3295939064766794222800490987520, 100204869963549181630558779565943580, 3070025447039504554088467623457608171520, 94632263448378916462441320194245442445186480
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OFFSET
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0,2
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COMMENTS
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A295456, defined by A295456(n) = (30*n)!*(5*n)!*(4*n)! / ((15*n)!*(12*n)!*(10*n)!*(2*n)!), is one of the 52 sporadic integral factorial ratio sequences of height 1 found by V. I. Vasyunin (see Bober, Table 2, Entry 26). Here we are essentially considering the sequence {A295456(n/2) : n >= 0}. Fractional factorials are defined in terms of the gamma function; for example, (5*n/2)! := Gamma(1 + 5*n/2).
This sequence is only conjecturally an integer sequence.
Conjecture: the supercongruences a(n*p^r) == a(n*p^(r-1)) (mod p^(3*r)) hold for all primes p >= 5 and all positive integers n and r.
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LINKS
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FORMULA
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a(n) ~ c^n * 1/sqrt(6*Pi*n), where c = 18750*sqrt(3).
a(n) = 4800*(15*n - 1)*(15*n - 7)*(15*n - 11)*(15*n - 13)*(15*n - 17)*(15*n - 19)*(15*n - 23)*(15*n - 29)/(n*(n - 1)*(3*n - 2)*(3*n - 4)*(6*n - 1)*(6*n - 5)*(6*n - 7)*(6*n - 11))*a(n-2) with a(0) = 1 and a(1) = 7168.
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MAPLE
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seq( simplify((15*n)!*(5*n/2)!*(2*n)!/((15*n/2)!*(6*n)!*(5*n)!*n!)), n = 0..15)
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CROSSREFS
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Cf. A276100, A276101, A276102, A295431, A295456, A347854, A347855, A347856, A347857, A347858, A364173 - A364185.
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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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