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A328510
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Smallest number whose divisors have n non-singleton runs.
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2
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1, 2, 20, 90, 630, 1260, 3780, 21420, 41580, 128520, 270270, 554400, 706860, 1413720, 2042040, 4324320, 4084080, 9189180, 6126120, 43825320, 12252240, 18378360, 82162080, 36756720, 85765680, 73513440, 183783600, 306306000, 257297040, 563603040, 514594080
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OFFSET
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0,2
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LINKS
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EXAMPLE
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The sequence of terms together with their non-singleton runs of divisors begins:
1: {}
2: {{1,2}}
20: {{1,2},{4,5}}
90: {{1,2,3},{5,6},{9,10}}
630: {{1,2,3},{5,6,7},{9,10},{14,15}}
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MATHEMATICA
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dv=Table[Length[DeleteCases[Length/@Split[Divisors[n], #2==#1+1&], 1]], {n, 1000}];
Table[Position[dv, i][[1, 1]], {i, Union[dv]}]
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CROSSREFS
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Equal {1} followed by the positions of first appearances in A328511 (times 2).
The longest run of divisors of n has length A055874.
Numbers whose divisors have no non-singleton runs are A005408.
The number of successive pairs of divisors of n is A129308(n).
The number of singleton runs of divisors is A132881.
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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Offset changed to 0 and a(10)-a(30) added by Giovanni Resta, Oct 25 2019
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STATUS
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approved
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