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A035274
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One fifth of deca-factorial numbers.
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9
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1, 15, 375, 13125, 590625, 32484375, 2111484375, 158361328125, 13460712890625, 1278767724609375, 134270611083984375, 15441120274658203125, 1930140034332275390625, 260568904634857177734375, 37782491172054290771484375, 5856286131668415069580078125
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OFFSET
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1,2
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COMMENTS
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a(n)= (Pochhammer(5/10,n)*10^n)/5.
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LINKS
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FORMULA
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5*a(n) = (10*n-5)(!^10) = Product_{j=1..n} (10*j-5).
E.g.f.: (-1 + (1-10*x)^(-1/2))/5.
a(n) = (Pochhammer(5/10,n)*10^n)/5.
Sum_{n>=1} 1/a(n) = exp(1/10)*sqrt(5*Pi/2)*erf(1/sqrt(10)), where erf is the error function. - Amiram Eldar, Dec 22 2022
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MAPLE
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seq( mul(10*j-5, j=1..n)/5, n=1..20); # G. C. Greubel, Nov 11 2019
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MATHEMATICA
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Table[10^n*Pochhammer[5/10, n]/5, {n, 20}] (* G. C. Greubel, Nov 11 2019 *)
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PROG
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(PARI) vector(20, n, prod(j=1, n, 10*j-5)/5 ) \\ G. C. Greubel, Nov 11 2019
(Magma) [(&*[10*j-5: j in [1..n]])/5: n in [1..20]]; // G. C. Greubel, Nov 11 2019
(Sage) [product( (10*j-5) for j in (1..n))/5 for n in (1..20)] # G. C. Greubel, Nov 11 2019
(GAP) List([1..20], n-> Product([1..n], j-> 10*j-5)/5 ); # G. C. Greubel, Nov 11 2019
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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