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A092170 Sum of squares of alternating factorials : n!^2 - (n-1)!^2 + (n-2)!^2 - ... 1!^2. 1
1, 3, 33, 543, 13857, 504543, 24897057, 1600805343, 130081089057, 13038108350943, 1580312813889057, 227862219988670943, 38547925823643969057, 7561506530728353470943, 1702450746193471070529057 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
The height of a regular simplex (hypertetrahedron) of dimension n and with unit length edges will be h(n)=sqrt(a(n))/n!. The contents (hypervolume) will then be V(n)=V(n-1)*h(n)/n where V(1)=1.
LINKS
FORMULA
a(n) = n!^2 - a(n-1), a(1)=1. - Charles R Greathouse IV, Oct 13 2004
EXAMPLE
a(3)=3!^2-a(2)=36-a(2);
a(2)=2!^2-a(1)=4-a(1)=3-1=3 ->
a(3)=36-3=33.
MATHEMATICA
a[n_] := Sum[(-1)^j*((n - j)!)^2, {j, 0, n - 1}]
Module[{nn=20, fctrls}, fctrls=(Range[nn]!)^2; Table[Total[Times@@@ Partition[ Riffle[Reverse[Take[fctrls, n]], {1, -1}, {2, -1, 2}], 2]], {n, nn}]] (* Harvey P. Dale, Aug 21 2016 *)
CROSSREFS
Sequence in context: A355795 A291818 A209245 * A083080 A002916 A009659
KEYWORD
easy,nonn
AUTHOR
Christer Mauritz Blomqvist (MauritzTortoise(AT)hotmail.com), Apr 01 2004
STATUS
approved

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Last modified May 21 11:59 EDT 2024. Contains 372736 sequences. (Running on oeis4.)