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Search: id:A093549
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| A093549 |
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a(n) is the smallest number m such that each of the numbers m-1, m and m+1 has n distinct prime divisors. |
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+0
5
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| 3, 21, 645, 37961, 1042405, 323567035, 30989984675, 10042712381261
(list; graph; listen)
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OFFSET
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1,1
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FORMULA
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a[n_] := (For[m=2, !(Length[FactorInteger[m-1]]==n && Length[FactorInteger[m]]==n&&Length[FactorInteger[m+1]]==n), m++ ];m)
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EXAMPLE
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a(3) =645 because 644=2^2*7*23; 645=3*5*43; 646=2*17*19
and 645 is the smallest number m such that each of the numbers
m-1, m & m+1 has 3 distinct prime divisors.
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MATHEMATICA
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a[n_] := (For[m=2, !(Length[FactorInteger[m-1]]==n && Length[FactorInteger[m]]==n&&Length[FactorInteger[m+1]]==n), m++ ]; m); Do[Print[a[n]], {n, 7}]
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CROSSREFS
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Cf. A093550, A052215, A093548.
Sequence in context: A135327 A128679 A111432 this_sequence A012044 A098918 A001699
Adjacent sequences: A093546 A093547 A093548 this_sequence A093550 A093551 A093552
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KEYWORD
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more,nonn
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AUTHOR
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Farideh Firoozbakht (mymontain(AT)yahoo.com), Apr 07 2004
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EXTENSIONS
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a(7) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Apr 07 2008
a(8) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Jan 15 2009
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