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Search: id:A100474
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| A100474 |
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a(0) = 1; a(n) is the smallest integer such that a(n) + a(n-1) has the first n distinct prime factors not used before in this construction. |
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1
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| 1, 5, 380, 96197, 58546472, 42588477041, 42945524659398, 62170660055541623, 133274332258941430724, 322874181064180119947025, 950049250593734799731643802, 4193776877793643794299905615515
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OFFSET
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0,2
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COMMENT
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a(11) is the first semiprime in the sequence. What is the next? After a(2) = 5, is there another prime?
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FORMULA
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a(n) - a(n-1) = primorial(triangular(n))/primorial(triangular(n-1)) = A002110(A000217(n))/A002110(A000217(n-1))
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EXAMPLE
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a(2) = 5 because 5 + a(1) = 2 * 3. a(3) = 380 because 380 + a(2) = 5 * 7 * 11. a(4) = 96197 (coincidentally the 3-brilliant 19 * 61 * 83) because 96197 + a(3) = 13 * 17 * 19 * 23.
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CROSSREFS
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Cf. A000040, A001358, A002110, A000217.
Sequence in context: A121668 A098038 A072172 this_sequence A060506 A057633 A006700
Adjacent sequences: A100471 A100472 A100473 this_sequence A100475 A100476 A100477
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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), Nov 22 2004
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