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A090905 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 first term of each group. 4
1, 2, 3, 5, 9, 15, 27, 47, 87, 167, 327, 635, 1263, 2519, 5007, 10007, 19947, 39875, 79739, 159399, 318779, 637503, 1274999, 2549979, 5099903, 10199787, 20399535, 40799063, 81598083, 163196135, 326392259, 652784499, 1305568943, 2611137839 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

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.

LINKS

Table of n, a(n) for n=1..34.

CROSSREFS

Cf. A090904, A090906, A090907.

Sequence in context: A067847 A190138 A022858 * A065956 A178738 A060013

Adjacent sequences:  A090902 A090903 A090904 * A090906 A090907 A090908

KEYWORD

nonn

AUTHOR

Amarnath Murthy, Dec 13 2003

EXTENSIONS

More terms from David Wasserman, Feb 10 2006

STATUS

approved

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Last modified December 17 22:43 EST 2014. Contains 252040 sequences.