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Search: id:A030450
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| A030450 |
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Related to number of elements in the free band (idempotent semigroup) on n generators. |
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+0
4
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| 1, 1, 4, 144, 331776, 2751882854400, 272622932796264897576960000, 3641839910835401567626683591527643364677019238400000000
(list; graph; listen)
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OFFSET
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0,3
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REFERENCES
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J. Howie, Fundamentals of Semigroup Theory, Oxford University Press 1995, p. 123.
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LINKS
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Index entries for sequences related to semigroups
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FORMULA
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Binomial transform is A005345. - Michael Somos Oct 22 2006
a(n)=(n*a(n-1))^2 if n>0. a(0)=1. - Michael Somos Oct 22 2006
a(n) = Product_{i=1..n} (n-i+1)^(2^i).
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MATHEMATICA
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s=1; lst={}; Do[AppendTo[lst, s*=s*=n], {n, 9}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Oct 20 2009]
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PROGRAM
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(PARI) {a(n)=if(n<0, 0, prod(i=1, n, (n-i+1)^2^i))} /* Michael Somos Oct 22 2006 */
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CROSSREFS
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Cf. A030449.
A052129(n)=n*a(n-1) if n>0.
Sequence in context: A069135 A138176 A055209 this_sequence A041629 A159197 A160470
Adjacent sequences: A030447 A030448 A030449 this_sequence A030451 A030452 A030453
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KEYWORD
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nonn
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AUTHOR
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marcel_j(AT)hilbert.maths.utas.edu.au (Marcel Jackson)
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