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A104201
Sums of straddle primes.
1
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
KEYWORD
easy,nonn
AUTHOR
Cino Hilliard, Mar 13 2005
STATUS
approved