A104201 Sums of straddle primes.

8, 12, 18, 18, 18, 24, 30, 30, 30, 36, 42, 42, 42, 52, 52, 52, 52, 52, 60, 68, 68, 68, 68, 68, 78, 78, 78, 84, 90, 90, 90, 100, 100, 100, 100, 100, 112, 112, 112, 112, 112, 120, 128, 128, 128, 128, 128, 138, 138, 138, 144, 152, 152, 152, 152, 152, 162, 162, 162, 172

Offset

4,1

Links

Charles R Greathouse IV, Table of n, a(n) for n = 4..10000

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 3+5 = 8 the first entry in the table.

Prog

(PARI) strad(n) = my (y, pp, np); for(x=1, n, y=composite(x); pp=precprime(y); np=nextprime(y); print1(pp+np", "))
composite(n) = my(c=1, x=1); while(c <= n, x++; if(!isprime(x), c++)); x
(PARI) list(lim)=my(v=List(), p=3, t); forprime(q=5, , t=p+q; if(t>lim, return(Vec(v))); for(i=2, q-p, listput(v, t)); p=q) \\ Charles R Greathouse IV, Jan 22 2016

Crossrefs

Sequence in context: A091523 A257162 A352880 * A036327 A340681 A051144

Adjacent sequences: A104198 A104199 A104200 * A104202 A104203 A104204

Keyword

easy,nonn

Author

Cino Hilliard, Mar 13 2005

Status

approved