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Search: id:A090906
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| A090906 |
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Group the natural numbers such that the n-th group product is a multiple of the (n-1)th group product. (1), (2),(3,4), (5,6,7,8),(9,10,11,12,13,14),(15,16,17,18,19,20,21,22,23,24,25,26),... Sequence contains the number of terms in each group. |
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+0
5
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| 1, 1, 2, 4, 6, 12, 20, 40, 80, 160, 308, 628, 1256, 2488, 5000, 9940, 19928, 39864, 79660, 159380, 318724, 637496, 1274980, 2549924, 5099884, 10199748, 20399528, 40799020, 81598052, 163196124, 326392240, 652784444, 1305568896, 2611137796
(list; graph; listen)
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OFFSET
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1,3
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COMMENT
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Conjecture: For n > 4 the last term of the n-th group is 2p where p is the largest prime in the (n-1)th group. And these are the Bertrand primes.
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FORMULA
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For n>4 a(n)= 2*(A006992(n)-A006992(n-1)) - Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Mar 05 2004
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CROSSREFS
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Cf. A090904, A090905, A090907.
Sequence in context: A134320 A107383 A078025 this_sequence A047141 A105541 A105536
Adjacent sequences: A090903 A090904 A090905 this_sequence A090907 A090908 A090909
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KEYWORD
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nonn
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AUTHOR
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Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Dec 13 2003
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EXTENSIONS
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More terms from Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Mar 05 2004
More terms from David Wasserman (wasserma(AT)spawar.navy.mil), Feb 10 2006
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