A134101 Odd nonprimes such that the prior odd number is not a prime but the next odd number is a prime.

27, 35, 51, 57, 65, 77, 87, 95, 125, 135, 147, 155, 161, 171, 177, 189, 209, 221, 237, 249, 255, 261, 267, 275, 291, 305, 329, 335, 345, 357, 365, 371, 377, 387, 395, 407, 417, 429, 437, 447, 455, 477, 485, 497, 507, 519, 539, 545, 555, 561, 567, 575, 585

Offset: 1

Author

Enoch Haga, Oct 08 2007

Keywords

• easy
• nonn

Examples

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

Links

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

Crossrefs

Cf. A134100 A134099 A083370 A124582 A007510.

Programs

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 *)

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

Extensions

Definition clarified by Harvey P. Dale, Jan 04 2015