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A111168
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Semiprimes S such that 2*S - 1 is also a semiprime.
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5
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25, 26, 33, 35, 39, 46, 58, 62, 65, 85, 93, 94, 111, 118, 119, 133, 134, 145, 146, 155, 161, 178, 183, 202, 206, 209, 214, 219, 226, 235, 237, 247, 249, 253, 259, 265, 267, 287, 291, 295, 299, 334, 335, 341, 361, 362, 377, 382, 386, 391, 393, 395, 407, 422
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Define an m-th degree Tomaszewski n-chain of the first (second) kind and length k to be a sequence of n-almost primes p(1) < p(2) < ... < p(k) such that s(i+1) = m*s(i) +(-) 1 for i = 1, ..., k-1. Notice that a 2nd degree Tomaszewski 1-chain of the first (second) kind is the familiar Cunningham chain of the first (second) kind.
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FORMULA
| {a(n)} = a(n) is an element of A001358 and 2*a(n)-1 is an element of A001358.
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EXAMPLE
| n s(n) s*2-1
1 25 = 5^2 49 = 7^2
2 26 = 2 * 13 51 = 3 * 17
3 33 = 3 * 11 65 = 5 * 13
4 35 = 5 * 7 69 = 3 * 23
5 39 = 3 * 13 77 = 7 * 11
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CROSSREFS
| Cf. A001358, A111153, A111170, A111171, A111173, A111176.
Sequence in context: A003996 A132415 A067810 * A195331 A175426 A045567
Adjacent sequences: A111165 A111166 A111167 * A111169 A111170 A111171
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KEYWORD
| easy,nonn
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AUTHOR
| Jonathan Vos Post (jvospost3(AT)gmail.com), Oct 21 2005
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EXTENSIONS
| Extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), Oct 22 2005
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