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Search: id:A131354
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| A131354 |
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Number of primes between successive tribonacci numbers. |
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+0
1
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| 0, 0, 0, 0, 1, 1, 1, 3, 5, 8, 13, 23, 38, 61, 109, 179, 312, 537, 920
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OFFSET
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0,8
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COMMENT
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This is to tribonacci numbers A000073 as A052011 is to Fibonacci numbers and as A052012 is to Lucas numbers A000204. It is mere coincidence that all values until a(12) = 38 are themselves Fibonacci. The formula plus the known asymptotic prime distribution gives the asymptotic approximation of this sequence, which is the same even if we use one of the alternative definitions of tribonacci with different initial values.
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FORMULA
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a(n) = A000720(A000073(n)) - A000720(A000073(n-1)).
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EXAMPLE
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Between Trib(8)=24 and Trib(9)=44 we find the following primes: 29, 31, 37, 41, 43, hence a(8)=5.
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CROSSREFS
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Cf. A000040, A000073, A052011, A052012, A056816.
Sequence in context: A020701 A024885 A133605 this_sequence A014252 A095223 A070948
Adjacent sequences: A131351 A131352 A131353 this_sequence A131355 A131356 A131357
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KEYWORD
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easy,nonn
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AUTHOR
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Jonathan Vos Post (jvospost2(AT)yahoo.com), Oct 21 2007
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