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 A151998 Directed genus of the binary de Bruijn graph D_n. 0
 0, 0, 0, 1, 2, 7, 15, 35, 75, 163, 337, 709, 1458, 3001, 6135, 12529, 25468, 51739, 104829, 212205, 428916, 866215, 1747527, 3523213, 7097895, 14291683, 28760643, 57852469, 116321445, 233798623, 469761015, 943591237, 1894836585, 3804113881, 7635493643 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,5 LINKS Table of n, a(n) for n=0..34. A. W. Hales and N. Hartsfield, The directed genus of the de Bruijn graph, Discrete Math., 309 (2009), 5259-5263. FORMULA See Maple code. MAPLE with(numtheory); f:=proc(n) local t1, t2, t3, i; t1:=divisors(n+2); t2:=convert(t1, list); t3:=add( phi(t2[i])*2^((n+2)/t2[i]), i =1..nops(t2)); 2^(n-1) + 1 - t3/(2*(n+2)); end; PROG (PARI) a(n) = 2^(n-1) + 1 - sumdiv(n+2, d, 2^((n+2)/d)*eulerphi(d))/(2*(n+2)); \\ Michel Marcus, Mar 02 2019 CROSSREFS Sequence in context: A209633 A216633 A295145 * A308631 A052130 A366130 Adjacent sequences: A151995 A151996 A151997 * A151999 A152000 A152001 KEYWORD nonn AUTHOR N. J. A. Sloane, Sep 15 2009 STATUS approved

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Last modified May 22 09:32 EDT 2024. Contains 372745 sequences. (Running on oeis4.)