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 A199932 Meanders of length n. 3
 1, 3, 5, 12, 17, 47, 65, 169, 279, 645, 1025, 2698, 4097, 9917, 17345, 39698, 65537, 161395, 262145, 624004, 1089007, 2449881, 4194305, 10097733, 16812683, 38754747, 69117097, 155178266, 268435457, 629929761, 1073741825, 2459703907, 4400500499, 9756737721 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS A meander is a closed curve drawn by arcs of equal length and central angles of equal magnitude, starting with a positively oriented arc. a(n) = 2^(n-1) + 1 iff n is prime. LINKS Peter Luschny, Meander. FORMULA a(n) = Sum_{d|n} A198060(d-1,n/d-1). MAPLE A199932 := proc(n) local d, k, j, i; add(add(add(add( (-1)^(j+i)*binomial(i, j)*binomial(n/d-1, k)^d*((n/d)/(k+1))^j, i=0..d-1), j=0..d-1), k=0..(n/d-1)), d=numtheory[divisors](n)) end: seq(A199932(i), i=1..34); MATHEMATICA A198060[m_, n_] := Sum[ Sum[ Sum[(-1)^(j+i)*Binomial[i, j]* Binomial[n, k]^(m+1)*(n+1)^j*(k+1)^(m-j)/(k+1)^m, {i, 0, m}], {j, 0, m}], {k, 0, n}]; a[n_] := Sum[ A198060[d-1, n/d-1], {d, Divisors[n]}]; Table[a[n], {n, 1, 34}] (* Jean-François Alcover, Jun 27 2013 *) CROSSREFS Cf. A198060, A200062. Sequence in context: A299490 A126471 A317100 * A305552 A226652 A024696 Adjacent sequences:  A199929 A199930 A199931 * A199933 A199934 A199935 KEYWORD nonn AUTHOR Peter Luschny, Nov 20 2011 STATUS approved

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Last modified June 12 07:43 EDT 2021. Contains 344943 sequences. (Running on oeis4.)