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A155747
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Smallest number m with property that 2^m-1 is divisible by first n odd primes.
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1
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2, 4, 12, 60, 60, 120, 360, 3960, 27720, 27720, 27720, 27720, 27720, 637560, 8288280, 240360120, 240360120, 240360120, 240360120, 240360120, 240360120, 9854764920, 9854764920, 19709529840, 98547649200, 1675310036400, 88791431929200
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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LINKS
| T. D. Noe, Table of n, a(n) for n=1..500
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FORMULA
| 2^m == 1 (mod (primorial(n)/2)) == 1 (mod (A002110(n+1)/2))
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EXAMPLE
| n=1, m=2, 2^2-1=3
n=2, m=4, 2^4-1=15=3*5
n=3, m=12, 2^12-1=4095=(3*5*7)*39
n=4, m=60, 2^60-1=1152921504606846975=(3*5*7*11)*998200436889045
n=5, m=60, 2^60-1=1152921504606846975=(3*5*7*11*13)*76784648991465
n=6, m=120, 2^120-1=1329227995784915872903807060280344575=
(3*5*7*11*13*17)*5207451355644026063755096120665.
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MATHEMATICA
| Table[LCM@@(MultiplicativeOrder[2, # ]& /@ Prime[Range[2, n]]), {n, 2, 50}] [From T. D. Noe (noe(AT)sspectra.com), May 07 2010]
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CROSSREFS
| A002110
Sequence in context: A177921 A128648 A128646 * A058254 A076244 A058255
Adjacent sequences: A155744 A155745 A155746 * A155748 A155749 A155750
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KEYWORD
| nonn
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AUTHOR
| Zak Seidov (zakseidov(AT)yahoo.com), Jan 26 2009
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EXTENSIONS
| a(16)-a(21) from D. S. McNeil (d.mcneil(AT)qmul.ac.uk), Mar 04 2009
Extended by T. D. Noe (noe(AT)sspectra.com), May 07 2010
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