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A001981
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Restricted partitions.
(Formerly M3832 N1572)
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5
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1, 1, 5, 13, 33, 73, 151, 289, 526, 910, 1514, 2430, 3788, 5744, 8512, 12346, 17575, 24591, 33885, 46029, 61731, 81805, 107233, 139143, 178870, 227930, 288100, 361384, 450096, 556834, 684572, 836618, 1016737, 1229093, 1478379, 1769773
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OFFSET
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0,3
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COMMENTS
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Number of partitions of 4n into up to 8 parts each no more than n; or partitions of 4n into up to n parts each no more than 8; or partitions of 5n into exactly n single-digit parts; or partitions of 4(n+2) into exactly 8 parts each no more than n+1; or partitions of 4(n+9) into exactly 8 distinct parts each no more than n+8; etc. Points lie on 252 different septics with the pattern repeating every 420 points, amounting to 4 sets of parallel septics depending on whether n mod 6 is in {0}, {1,5}, {2,4} or {3}.
Also, the dimension of the vector space of homogeneous covariants of degree n for the binary form of degree 8. - Leonid Bedratyuk, Dec 06 2006
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REFERENCES
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A. Cayley, Numerical tables supplementary to second memoir on quantics, Collected Mathematical Papers. Vols. 1-13, Cambridge Univ. Press, London, 1889-1897, Vol. 2, pp. 276-281.
Hilbert, D., Theory of algebraic invariants. Lectures. Cambridge University Press, (1993).
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
Springer, T.A., Invariant theory, Lecture Notes in Mathematics, 585, Springer-Verlag, (1977).
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LINKS
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FORMULA
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a(n) =A067059(n, 8) =A067059(8, n) =(1/152409600) * (1812n^7 + 57078n^6 + 748314n^5 + 5278770n^4 + 21727272n^3 + 52982181n^2 + 77609245n + 66220839 + (297675n^2+2679075n+27088425)*(1, -1)pcr(n, 2) + (1254400*n+5644800)*(2, -1, -1)pcr(n, 3) + 9408000*(0, -1, 1)pcr(n, 3) + 4762800*(1, 1, -1, -1)pcr(n, 4) + 24385536*(1, -1, 0, 0, 0)pcr(n, 5) + 6220800(3, -1, 2, -2, 1, -3, 0)pcr(n, 7)) where for example (0, -1, 1)pcr(n, 3) means the value 0 if n mod 3 = 0, the value -1 if n mod 3 = 1 and the value 1 if n mod 3 = 2. - Henry Bottomley, Jul 19 2003
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EXAMPLE
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a(3)=13 since partitions of 12 into up to 8 parts each no more than 3 are 3+3+3+3 = 3+3+3+2+1 = 3+3+3+1+1+1 = 3+3+2+2+2 = 3+3+2+2+1+1 = 3+3+2+1+1+1+1 = 3+3+1+1+1+1+1+1 = 3+2+2+2+2+1 = 3+2+2+2+1+1+1 = 3+2+2+1+1+1+1+1 = 2+2+2+2+2+2 = 2+2+2+2+2+1+1 = 2+2+2+2+1+1+1+1; or equivalently partitions of 15 into exactly 3 single-digit numbers are 9+5+1 = 9+4+2 = 9+3+3 = 8+6+1 = 8+5+2 = 8+4+3 = 7+7+1 = 7+6+2 = 7+5+3 = 7+4+4 = 6+6+3 = 6+5+4 =5+5+5.
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MAPLE
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a:= n-> subs({x=1}, convert(series((product('1-x^i', 'i'=9..8+n)/ product('1-x^k', 'k'=2..n)), x, 4*n+1), polynom)): seq (a(n), n=0..40); # Leonid Bedratyuk, Dec 06 2006
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MATHEMATICA
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a[n_] := Length[IntegerPartitions[4*n, 8, Range[n]]]; Table[a[n], {n, 0, 40}] (* Jean-François Alcover, Mar 17 2014 *)
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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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