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Search: id:A115392
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| A115392 |
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First appearance of n-th prime as prime factor in list of semiprimes. |
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+0
1
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| 1, 2, 4, 5, 8, 10, 12, 14, 16, 21, 22, 25, 27, 29, 33, 35, 38, 41, 45, 47, 50, 52, 55, 58, 62, 64, 67, 70, 73, 76, 82, 84, 87, 88, 93, 96, 100, 104, 107, 111, 113, 115, 120, 121, 124, 126, 133, 137, 141, 142, 143, 147, 149, 155, 158, 162, 168, 169, 174, 176, 178, 183
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Let s(n) = n-th semiprime = p*q, "new" shows prime factor not appearing before, and a(n) is place of first appearing of n-th prime, a(n) is in sequence.
n : 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, ...
s(n): 4, 6, 9, 10, 14, 15, 21, 22, 25, 26, 33, 34, ...
p*q: 2*2, 2*3, 3*3, 2*5, 2*7, 3*5, 3*7, 2*11, 5*5, 2*13, 3*11, 2*17, ...
new: 2, 3, 5, 7, 11, 13, 17, ...
a(n): 1, 2, 4, 5, 8, 10, 12, ...
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EXAMPLE
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a(5)=8 because 5-th prime, 11, first appeared as a prime factor in 8-th semiprime 22=2*11; a(6)=10 because 6-th prime, 13, first appeared as a prime factor in 10-th semiprime 26=2*13 etc.
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CROSSREFS
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Sequence in context: A047612 A123886 A005242 this_sequence A007729 A144876 A072437
Adjacent sequences: A115389 A115390 A115391 this_sequence A115393 A115394 A115395
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KEYWORD
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nonn
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AUTHOR
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Zak Seidov (zakseidov(AT)yahoo.com), Mar 08 2006
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