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A038780
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An intermediate sequence for counting nonisomorphic circulant directed p^2-graphs, indexed by odd primes p.
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2
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9, 36, 196, 11664, 123904, 16941456, 213218404, 36384036516, 91921690256400, 1281107924034624, 3643830108147610000, 755580082985683928064, 10965324181121364597904, 2340151860941299402849476, 7500891349210337560308603456, 24695823438181435496869784039184
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OFFSET
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1,1
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LINKS
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FORMULA
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a(n) = ( (1/(p-1)) * Sum_{r|p-1} phi(r) * 2^((p-1)/r) )^2 where p = prime(n+1). - Sean A. Irvine, Feb 14 2021
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PROG
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(PARI) a(n) = my(p=prime(n+1)); (((1/(p-1)) * sumdiv(p-1, r, eulerphi(r) * 2^((p-1)/r)))^2); \\ Sean A. Irvine, Feb 14 2021
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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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EXTENSIONS
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STATUS
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approved
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