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A159557
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Number of elements in the mutation class of any quiver of type D_n.
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1
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4, 6, 26, 80, 246, 810, 2704, 9252, 32066, 112720, 400024, 1432860, 5170604, 18784170, 68635478, 252088496, 930138522, 3446167860, 12815663844, 47820447028, 178987624514, 671825133648, 2528212128776, 9536895064400
(list; graph; refs; listen; history; internal format)
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OFFSET
| 3,1
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COMMENTS
| Table 1, p.15 of Buan, et al.
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LINKS
| Aslak Bakke Buan, Hermund Andre' Torkildsen, The number of elements in the mutation class of a quiver of type D_n, version 2, Apr 14, 2009.
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FORMULA
| a(n) = 6 if n = 4; a(n) = SUM[d|n] (phi(n/d))C(2d,d)/(2n) where phi is the Euler function, when n>4. For n>4 a(n) = SUM[d|n] A000010(n/d)*A000984(d)/(2*n)
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MAPLE
| A159557 := proc(n) if n = 3 then 4; elif n = 4 then 6; else add( numtheory[phi](n/d)*binomial(2*d, d), d=numtheory[divisors](n))/2/n ; fi; end: seq(A159557(n), n=3..40) ; [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Apr 16 2009]
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CROSSREFS
| Cf. A000010, A000984.
Sequence in context: A024471 A075277 A192874 * A176756 A054094 A123873
Adjacent sequences: A159554 A159555 A159556 * A159558 A159559 A159560
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KEYWORD
| nonn,uned
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AUTHOR
| Jonathan Vos Post (jvospost3(AT)gmail.com), Apr 15 2009
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EXTENSIONS
| More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Apr 16 2009
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