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A318729
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Number of cyclic compositions (necklaces of positive integers) summing to n that have only one part or whose consecutive parts (including the last with first) are indivisible.
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13
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1, 1, 1, 1, 2, 1, 3, 2, 4, 6, 6, 8, 11, 19, 21, 30, 41, 59, 79, 112, 157, 219, 305, 430, 605, 860, 1210, 1727, 2424, 3463, 4905, 7001, 9954, 14211, 20271, 28980, 41392, 59254, 84800, 121540, 174163, 249932, 358578, 515091, 739933, 1063827, 1529767, 2201383
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OFFSET
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1,5
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LINKS
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FORMULA
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EXAMPLE
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The a(13) = 11 cyclic compositions with successive parts indivisible:
(13)
(2,11) (3,10) (4,9) (5,8) (6,7)
(2,4,7) (2,6,5) (2,8,3) (3,6,4)
(2,3,5,3)
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MATHEMATICA
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neckQ[q_]:=Array[OrderedQ[{q, RotateRight[q, #]}]&, Length[q]-1, 1, And];
Table[Length[Select[Join@@Permutations/@IntegerPartitions[n], Or[Length[#]==1, neckQ[#]&&And@@Not/@Divisible@@@Partition[#, 2, 1, 1]]&]], {n, 20}]
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PROG
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(PARI)
b(n, q, pred)={my(M=matrix(n, n)); for(k=1, n, M[k, k]=pred(q, k); for(i=1, k-1, M[i, k]=sum(j=1, k-i, if(pred(j, i), M[j, k-i], 0)))); M[q, ]}
seq(n)={my(v=sum(k=1, n, k*b(n, k, (i, j)->i%j<>0))); vector(n, n, 1 + sumdiv(n, d, eulerphi(d)*v[n/d])/n)} \\ Andrew Howroyd, Oct 27 2019
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CROSSREFS
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Cf. A000740, A008965, A059966, A167606, A285573, A303362, A304713, A316476, A318726, A318727, A318728, A318730, A328600.
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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