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A082425
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a(1)=1, a(n) = -1 + n*Sum_{j=1..n-1} a(j).
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3
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1, 1, 5, 27, 169, 1217, 9939, 90871, 920069, 10222989, 123698167, 1619321459, 22805443881, 343835923129, 5525934478859, 94309281772527, 1703461402016269, 32465970250192421, 651123070017747999, 13707854105636799979
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OFFSET
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1,3
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LINKS
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FORMULA
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For n >= 2, a(n) = floor(n*(3-e)*n!).
In the following remarks we use an offset of 1, i.e., a(1) = 1, a(2) = 1, a(3) = 5, ... .
For n >= 2, a(n) = n*n!*Sum_{k = 2..n} 1/(k*(k-1)*k!).
For n >= 2, a(n) = 3*n*n! - Sum_{k = 0..n} (k+1)!*binomial(n,k).
Limit_{n -> oo} a(n)/(n*n!) = 3 - e.
E.g.f.: 1 + t + (3*t - exp(t))/(1-t)^2.
Recurrence relation: a(1) = 1, a(2) = 1, a(3) = 5, a(n) = (n+2)*a(n-1) - (n-1)*a(n-2) for n >= 4.
Recurrence relation: a(1) = 1, a(2) = 1, a(n) = (n^2*a(n-1) + 1)/(n-1) for n >= 2.
The recurrence relation x(n) = (n^2*x(n-1) - 1)/(n-1), for n >= 2, has the general solution x(n) = n*n!*x(1) - a(n); particular solutions are A007808 (x(1) = 1) and A001339 (x(1) = 3). (End)
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MAPLE
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a:= n -> n*n!*add(1/(k*(k-1)*k!), k = 2..n): seq(a(n), n = 2..20); # Peter Bala, Jul 09 2008
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MATHEMATICA
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a[n_]:= a[n]= If[n<3, 1, -1 +n*Sum[a[j], {j, n-1}]];
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PROG
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(Magma) [n le 2 select 1 else (n^2*Self(n-1) +1)/(n-1): n in [1..30]]; // G. C. Greubel, Feb 03 2024
(SageMath)
def a(n): return 1 if (n==1) else -1 + n*sum(a(j) for j in range(1, n))
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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