A104202 Differences of straddle primes.

2, 2, 4, 4, 4, 2, 4, 4, 4, 2, 4, 4, 4, 6, 6, 6, 6, 6, 2, 6, 6, 6, 6, 6, 4, 4, 4, 2, 4, 4, 4, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 2, 6, 6, 6, 6, 6, 4, 4, 4, 2, 6, 6, 6, 6, 6, 4, 4, 4, 6, 6, 6, 6, 6, 8, 8, 8, 8, 8, 8, 8, 4, 4, 4, 2, 4, 4, 4, 2, 4, 4, 4, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 4, 4, 4, 6

Offset

4,1

Links

Table of n, a(n) for n=4..102.

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 5-3 = 2 the first entry in the table.

Mathematica

NextPrime[#]-NextPrime[#, -1]&/@Rest[Select[Range[200], !PrimeQ[#]&]] (* Harvey P. Dale, Aug 23 2012 *)

Prog

(PARI) straddiff(n) = { local (x, y, pp, np); for(x=1, n, y=composite(x); pp=precprime(y); np=nextprime(y); print1(np-pp", ") )
composite(n) = { local(c, x); c=1; x=1; while(c <= n, x++; if(!isprime(x), c++); ); return(x) } }

Crossrefs

Sequence in context: A006460 A064137 A329588 * A042946 A037202 A227091

Adjacent sequences: A104199 A104200 A104201 * A104203 A104204 A104205

Keyword

easy,nonn

Author

Cino Hilliard, Mar 13 2005

Status

approved