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A335459
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Number of permutations of the prime indices of n! with at least one non-singleton run.
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3
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0, 0, 0, 0, 4, 18, 102, 786, 3960, 51450, 675570, 10804710, 139674024, 2793377664, 58662908640, 1798893694080, 26985313555200, 782574083010720, 25992638958686400, 857757034323189000, 30021498596590300800, 1563341714743040232000, 64179292280096037844800, 2631350957341279888915200
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OFFSET
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0,5
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COMMENTS
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A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.
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LINKS
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FORMULA
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EXAMPLE
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The a(4) = 4 and a(5) = 18 permutations:
(1,1,1,2) (1,1,1,2,3)
(1,1,2,1) (1,1,1,3,2)
(1,2,1,1) (1,1,2,1,3)
(2,1,1,1) (1,1,2,3,1)
(1,1,3,1,2)
(1,1,3,2,1)
(1,2,1,1,3)
(1,2,3,1,1)
(1,3,1,1,2)
(1,3,2,1,1)
(2,1,1,1,3)
(2,1,1,3,1)
(2,1,3,1,1)
(2,3,1,1,1)
(3,1,1,1,2)
(3,1,1,2,1)
(3,1,2,1,1)
(3,2,1,1,1)
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MATHEMATICA
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primeMS[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
Table[Length[Select[Permutations[primeMS[n!]], MatchQ[#, {___, x_, x_, ___}]&]], {n, 0, 10}]
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PROG
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a(n)={my(sig=factor(n!)[, 2]); vecsum(sig)!/vecprod([k! | k<-sig]) - count(sig)} \\ Andrew Howroyd, Apr 17 2021
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CROSSREFS
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Permutations of prime indices are A008480.
Permutations of prime indices of n! are A325617.
Anti-run permutations of prime indices are A335452.
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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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