A104200 Upper bound on a straddle prime pair.

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.

Links

Table of n, a(n) for n=4..73.

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

Adjacent sequences: A104197 A104198 A104199 * A104201 A104202 A104203

Keyword

easy,nonn

Author

Cino Hilliard, Mar 13 2005

Status

approved