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A288171
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Lexicographically earliest sequence of distinct positive terms such that, for any n > 0, a(n)*a(n+3) has at least 5 distinct prime factors.
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3
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1, 2, 3, 2310, 1155, 770, 4, 6, 9, 1365, 385, 910, 8, 12, 11, 1785, 455, 210, 10, 18, 13, 231, 595, 330, 20, 22, 7, 273, 105, 390, 30, 26, 14, 77, 165, 195, 60, 28, 34, 91, 255, 285, 66, 38, 42, 35, 315, 55, 78, 44, 84, 70, 345, 65, 33, 52, 102, 130, 357, 95
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history;
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OFFSET
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1,2
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COMMENTS
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This sequence is a permutation of the natural numbers, with inverse A288800.
See also A288164 for similar sequences.
Conjecturally, a(n) ~ n.
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LINKS
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Rémy Sigrist, Table of n, a(n) for n = 1..25000
Rémy Sigrist, C++ program for A288171
Index entries for sequences that are permutations of the natural numbers
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EXAMPLE
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The first terms, alongside the primes p dividing a(n)*a(n+3), are:
n a(n) p
-- ---- --------------
1 1 2, 3, 5, 7, 11
2 2 2, 3, 5, 7, 11
3 3 2, 3, 5, 7, 11
4 2310 2, 3, 5, 7, 11
5 1155 2, 3, 5, 7, 11
6 770 2, 3, 5, 7, 11
7 4 2, 3, 5, 7, 13
8 6 2, 3, 5, 7, 11
9 9 2, 3, 5, 7, 13
10 1365 2, 3, 5, 7, 13
11 385 2, 3, 5, 7, 11
12 910 2, 5, 7, 11, 13
13 8 2, 3, 5, 7, 17
14 12 2, 3, 5, 7, 13
15 11 2, 3, 5, 7, 11
16 1785 2, 3, 5, 7, 17
17 455 2, 3, 5, 7, 13
18 210 2, 3, 5, 7, 13
19 10 2, 3, 5, 7, 11
20 18 2, 3, 5, 7, 17
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CROSSREFS
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Cf. A288164, A288800 (inverse).
Sequence in context: A323518 A004909 A266585 * A137321 A066848 A324310
Adjacent sequences: A288168 A288169 A288170 * A288172 A288173 A288174
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KEYWORD
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nonn,look
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AUTHOR
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Rémy Sigrist, Jun 16 2017
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STATUS
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approved
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