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A107392
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Number of (inequivalent) fuzzy subgroups of the direct sum of group of integers modulo p^n and group of integers modulo 2 for a prime p with (p,2) = 1. Z_{p^n} + Z_2.
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5
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7, 31, 103, 303, 831, 2175, 5503, 13567, 32767, 77823, 182271, 421887, 966655, 2195455, 4947967, 11075583, 24641535, 54525951, 120061951, 263192575, 574619647, 1249902591, 2709520383, 5855248383, 12616466431, 27111981055, 58116276223, 124285616127
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OFFSET
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0,1
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COMMENTS
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This is just one row of a double sequence a(n,m) for n = 0,1,2, ... and m = 0,1,2,...: a(n,m) = 2^(n+m+1)*(Sum_{r=0..m} (2^(-r) * binomial(n, n-r)* binomial(m, r))) - 1, with 0 <= m <= n and a(0,0)=1.
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LINKS
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FORMULA
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a(n) = (2^n)*(n^2 + 7n + 8) - 1 for n=0..14.
G.f.: (12*x^2 - 18*x + 7) / ((x-1)*(2*x-1)^3). - Colin Barker, Jan 15 2015
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EXAMPLE
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a(3) = 303. A fuzzy subgroup is simply a chain of subgroups in the lattice of subgroups. Counting of chains in the lattice of subgroups of Z_{p^3} + Z_2 gives us a(3) = 303. The two papers cited describe the counting process using fuzzy subgroup concept.
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MATHEMATICA
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LinearRecurrence[{7, -18, 20, -8}, {7, 31, 103, 303}, 30] (* Harvey P. Dale, Dec 31 2015 *)
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PROG
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(PARI) Vec((12*x^2-18*x+7)/((x-1)*(2*x-1)^3) + O(x^100)) \\ Colin Barker, Jan 15 2015
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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Venkat Murali (v.murali(AT)ru.ac.za), May 25 2005
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EXTENSIONS
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STATUS
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approved
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