OFFSET
1,1
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
a(1)=27 because this odd nonprime is followed by the prime 29 but preceded by the odd nonprime 25.
MATHEMATICA
Select[Range[5, 1000, 2], !PrimeQ[#]&&!PrimeQ[#-2]&&PrimeQ[#+2]&] (* Vladimir Joseph Stephan Orlovsky, Feb 03 2012 *)
Transpose[Select[Partition[Range[1, 601, 2], 3, 1], Boole[PrimeQ[#]]=={0, 0, 1}&]] [[2]] (* or *) 2#+1&/@Flatten[Position[Partition[Boole[PrimeQ[ Range[ 1, 601, 2]]], 3, 1], _?(#=={0, 0, 1}&)]] (* Harvey P. Dale, Jan 04 2015 *)
PROG
(UBASIC) 10 'primes using counters 20 N=3:print "2 "; :print "3 "; :C=2 30 A=3:S=sqrt(N) 40 B=N\A 50 if B*A=N then 55 55 Q=N-2:R=N+2: if Q<>prmdiv(Q) and N<>prmdiv(N) and R=prmdiv(R) then print Q; N; R; "-"; :stop:else N=N+2:goto 30 60 A=A+2 70 if A<=sqrt(N) then 40:stop 81 C=C+1 100 N=N+2:goto 30
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Enoch Haga, Oct 08 2007
EXTENSIONS
Definition clarified by Harvey P. Dale, Jan 04 2015
STATUS
approved