1,1

Harvey P. Dale, Table of n, a(n) for n = 1..1000

a(1)=27 because this odd nonprime is followed by the prime 29 but preceded by the odd nonprime 25.

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 *)

(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

Cf. A134100 A134099 A083370 A124582 A007510.

Sequence in context: A072492 A164376 A025583 * A226191 A098883 A326893

Adjacent sequences: A134098 A134099 A134100 * A134102 A134103 A134104

easy,nonn

Enoch Haga, Oct 08 2007

Definition clarified by Harvey P. Dale, Jan 04 2015

approved