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Search: id:A123255
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| A123255 |
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Numbers n such that 4n+1, 4n+2, 4n+3 are all semiprimes. |
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1
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| 8, 21, 23, 30, 35, 50, 53, 54, 75, 98, 111, 158, 174, 210, 230, 260, 284, 315, 350, 410, 440, 459, 473, 485, 495, 525, 545, 554, 576, 590, 608, 615, 629, 660, 683, 774, 846, 900, 923, 966, 975, 989, 1071
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OFFSET
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1,1
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COMMENT
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4n+4 = 4*(n+1) = 2 * 2 *(n+1) cannot be semiprime as well, as it has at least 3 prime factors with multiplicity. Thus there are no four consecutive semiprimes.
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FORMULA
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{n: 4n+1 is in A001358 AND 4n+2 is in A001358 AND 4n+3 is in A001358}. {n: 4n+1 is in A070552 AND 4n+2 is in A070552}. {(A056809(i)-1)/4}.
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EXAMPLE
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a(1) = 8 because 4*8+1 = 33 = 3 * 11 is semiprime, and 4*8+2 = 34 = 2 * 17 is semiprime, and 4*8+3 = 35 = 3 * 5 is semiprime.
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CROSSREFS
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Cf. A001358, A056809, A070552.
Sequence in context: A079386 A130021 A003864 this_sequence A053750 A003249 A134862
Adjacent sequences: A123252 A123253 A123254 this_sequence A123256 A123257 A123258
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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 09 2006
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