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A104200
Upper bound on a straddle prime pair.
0
5, 7, 11, 11, 11, 13, 17, 17, 17, 19, 23, 23, 23, 29, 29, 29, 29, 29, 31, 37, 37, 37, 37, 37, 41, 41, 41, 43, 47, 47, 47, 53, 53, 53, 53, 53, 59, 59, 59, 59, 59, 61, 67, 67, 67, 67, 67, 71, 71, 71, 73, 79, 79, 79, 79, 79, 83, 83, 83, 89, 89, 89, 89, 89, 97, 97, 97, 97, 97, 97
OFFSET
4,1
COMMENTS
Straddle primes that occur only once on either side of the composite number are lower and upper twin primes respectively.
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.
PROG
(PARI) strad(n) = { local (x, y, pp, np); for(x=1, n, y=composite(x); pp=precprime(y); np=nextprime(y); print1(np", ") ) }
CROSSREFS
Sequence in context: A277777 A254930 A317769 * A249916 A115044 A206770
KEYWORD
easy,nonn
AUTHOR
Cino Hilliard, Mar 13 2005
STATUS
approved