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A145386
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a(1) = 1; a(n) = a(n-1)*(2*(n-1)+a(n-1)) for n > 1.
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0
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OFFSET
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1,2
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COMMENTS
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Next term has 89 decimal digits and is too large to include. - Klaus Brockhaus, Oct 13 2008
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LINKS
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FORMULA
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a(n) = Product_{k = 1..n} b(k), where b(1) = 1 and b(n) = a(n-1) + 2*(n-1) for n > 1. The sequence b(n) begins [1, 3, 7, 27, 575, 326035, ...] and is given by the recurrence b(n) = b(n-1)^2 - 2*(n-2)*b(n-1) + 2*(n-1) with b(1) = 1. - Peter Bala, Mar 27 2018
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EXAMPLE
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MATHEMATICA
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lst={}; s=1; Do[s*=(n+=s+n); AppendTo[lst, s], {n, 0, 7}]; lst
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PROG
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(ARIBAS) a:=1; for n:=1 to 9 do a:=a*(a+2*(n-1)); write(a:group(0), ", "); end; end; (* Klaus Brockhaus, Oct 13 2008 *)
(PARI) a=vector(15); a[1]=1; for(n=2, #a, a[n] = a[n-1]*(2*(n-1)+a[n-1])); a \\ Altug Alkan, Mar 27 2018
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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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EXTENSIONS
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STATUS
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approved
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