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Search: id:A104201
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| A104201 |
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Sums of straddle primes. |
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+0
1
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| 8, 12, 18, 18, 18, 24, 30, 30, 30, 36, 42, 42, 42, 52, 52, 52, 52, 52, 60, 68, 68, 68, 68, 68, 78, 78, 78, 84, 90, 90, 90, 100, 100, 100, 100, 100, 112, 112, 112, 112, 112, 120, 128, 128, 128, 128, 128, 138, 138, 138, 144, 152, 152, 152, 152, 152, 162, 162, 162, 172
(list; graph; listen)
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OFFSET
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4,1
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FORMULA
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Straddle primes are the nearest primes preceding and following composite n.
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EXAMPLE
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The first straddle prime pair is 3 and 5 which straddles the composite number
4 and 3+5 = 8 the first entry in the table.
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PROGRAM
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(PARI) \Straddle primes - largest prime preceding composite n and smallest \prime following n. strad(n) = { local (x, y, pp, np); for(x=1, n, y=composite(x); pp=precprime(y); np=nextprime(y); print1(pp+np", ") ) composite(n) = \ The n-th composite number. 1 is defined as as neither prime nor composite. { local(c, x); c=1; x=1; while(c <= n, x++; if(!isprime(x), c++); ); return(x) } }
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CROSSREFS
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Sequence in context: A129150 A030752 A091523 this_sequence A036327 A051144 A067537
Adjacent sequences: A104198 A104199 A104200 this_sequence A104202 A104203 A104204
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KEYWORD
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easy,nonn
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AUTHOR
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Cino Hilliard (hillcino368(AT)gmail.com), Mar 13 2005
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