A104199 Lower bound on a straddle prime pair.

3, 5, 7, 7, 7, 11, 13, 13, 13, 17, 19, 19, 19, 23, 23, 23, 23, 23, 29, 31, 31, 31, 31, 31, 37, 37, 37, 41, 43, 43, 43, 47, 47, 47, 47, 47, 53, 53, 53, 53, 53, 59, 61, 61, 61, 61, 61, 67, 67, 67, 71, 73, 73, 73, 73, 73, 79, 79, 79, 83, 83, 83, 83, 83, 89, 89, 89, 89, 89, 89, 89

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..74.

Formula

Straddle primes are the nearest primes preceding and following a composite number n.

Example

The first straddle prime pair is 3 and 5 which straddle the composite number 4.

Prog

(PARI) strad(n) = { my(y, pp, np); for(x=1, n, y=composite(x); pp=precprime(y); np=nextprime(y); print1(pp", ") ) }

Crossrefs

Sequence in context: A342622 A211517 A254935 * A103470 A316852 A357274

Adjacent sequences: A104196 A104197 A104198 * A104200 A104201 A104202

Keyword

easy,nonn

Author

Cino Hilliard, Mar 13 2005

Status

approved