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A035272
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One third of deca-factorial numbers.
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9
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1, 13, 299, 9867, 424281, 22486893, 1416674259, 103417220907, 8583629335281, 798277528181133, 82222585402656699, 9291152150500206987, 1142811714511525459401, 151993958030032886100333, 21735135998294702712347619, 3325475807739089514989185707, 542052556661471590943237270241
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OFFSET
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1,2
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LINKS
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FORMULA
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3*a(n) = (10*n-7)(!^10) = Product_{j=1..n} (10*j-7).
E.g.f.: (-1 + (1-10*x)^(-3/10))/3.
Sum_{n>=1} 1/a(n) = 3*(e/10^7)^(1/10)*(Gamma(3/10) - Gamma(3/10, 1/10)). - Amiram Eldar, Dec 22 2022
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MAPLE
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seq( mul(10*j-7, j=1..n)/3, n=1..20); # G. C. Greubel, Nov 11 2019
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MATHEMATICA
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Table[10^n*Pochhammer[3/10, n]/3, {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-7)/3 ) \\ G. C. Greubel, Nov 11 2019
(Magma) [(&*[10*j-7: j in [1..n]])/3: n in [1..20]]; // G. C. Greubel, Nov 11 2019
(Sage) [product( (10*j-7) for j in (1..n))/3 for n in (1..20)] # G. C. Greubel, Nov 11 2019
(GAP) List([1..20], n-> Product([1..n], j-> 10*j-7)/3 ); # 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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