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A136184
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Number of metacyclic groups of order 2^n.
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3
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1, 2, 4, 8, 12, 19, 26, 37, 48, 63, 78, 98, 117, 142, 166, 196, 225, 261, 295, 337, 377, 425, 471, 526, 578, 640, 699, 768, 834, 911, 984, 1069, 1150, 1243, 1332, 1434, 1531, 1642, 1748, 1868, 1983, 2113, 2237, 2377, 2511, 2661, 2805, 2966, 3120, 3292, 3457
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OFFSET
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1,2
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COMMENTS
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For number of metacyclic groups of order p^n, prime p >= 3, see A136185.
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LINKS
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FORMULA
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G.f.: -x*(x^10 + x^9 - x^8 + x^6 - x^3 - x - 1)/((x - 1)^4*(x + 1)^2*(x^2 + x + 1)).
For n > 3, a(n) = (n^3 + 48*n^2 - c*n + d)/72, where c = 168 or 177 for n even/odd, and d = 432, 416 or 424 for n = 0, 1 or 2 (mod 3), according to the Liedahl paper. Since this would yield (4,4,5) for n=1,2,3, one can simply add [n<4]*(n-4) to get a formula valid for all n. - M. F. Hasler, Jan 13 2015
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EXAMPLE
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a(3) = 4 since there are four metacyclic groups of order 2^3; they have invariants <3, 0, 0, 3, [ 8 ], >, <1, 2, 1, 1, [ 2, 4 ], >, <1, 1, 1, 2, [ 2 ], Dihedral> and <1, 1, 1, 2, [ 2 ], Quaternion> resp. (for details see MAGMA link).
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MATHEMATICA
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LinearRecurrence[{1, 2, -1, -2, -1, 2, 1, -1}, {1, 2, 4, 8, 12, 19, 26, 37, 48, 63, 78}, 60] (* Harvey P. Dale, May 31 2019 *)
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PROG
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(Magma) [ NumberOfMetacyclicPGroups(2, n): n in [1..51] ];
(PARI) A136184(n)=if(n<4, 2^(n-1), (((n+48)*n-[168, 177][1+n%2])*n+[432, 416, 424][1+n%3])/72) \\ M. F. Hasler, Jan 13 2015
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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