

A104202


Differences of straddle primes.


0



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
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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 53 = 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(nppp", ") )
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



