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 A104201 Sums of straddle primes. 0
 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; refs; listen; history; text; internal format)
 OFFSET 4,1 LINKS FORMULA Straddle primes are the nearest primes preceding and following composite n. EXAMPLE 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. PROG (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 neither prime nor composite. { local(c, x); c=1; x=1; while(c <= n, x++; if(!isprime(x), c++); ); return(x) } } CROSSREFS Sequence in context: A175975 A030752 A091523 * A036327 A051144 A067537 Adjacent sequences:  A104198 A104199 A104200 * A104202 A104203 A104204 KEYWORD easy,nonn AUTHOR Cino Hilliard (hillcino368(AT)gmail.com), Mar 13 2005 STATUS approved

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