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A134101 Odd nonprimes such that the prior odd number is not a prime but the next odd number is a prime. 5
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
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
Sequence in context: A072492 A164376 A025583 * A226191 A098883 A326893
KEYWORD
easy,nonn
AUTHOR
Enoch Haga, Oct 08 2007
EXTENSIONS
Definition clarified by Harvey P. Dale, Jan 04 2015
STATUS
approved

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Last modified April 21 14:03 EDT 2024. Contains 371870 sequences. (Running on oeis4.)