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A134099
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Odd nonprimes that are preceded by but not followed by primes.
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5
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25, 33, 49, 55, 63, 75, 85, 91, 115, 133, 141, 153, 159, 169, 175, 183, 201, 213, 235, 243, 253, 259, 265, 273, 285, 295, 319, 333, 339, 355, 361, 369, 375, 385, 391, 403, 411, 423, 435, 445, 451, 469, 481, 493, 505, 511, 525, 543, 549, 559, 565, 573, 579
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OFFSET
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1,1
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COMMENTS
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Primes referred to in the example are found in A124582 (see A083370 and compare A124582).
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LINKS
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Vincenzo Librandi, Table of n, a(n) for n = 1..1000
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EXAMPLE
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a(1) = 25 because it is an odd nonprime preceded by the prime 23 and followed by the odd nonprime 27.
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MATHEMATICA
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Select[Range[5, 1000, 2], !PrimeQ[#] && PrimeQ[#-2] && !PrimeQ[#+2]&] (* Vladimir Joseph Stephan Orlovsky, Feb 03 2012 *)
2#-1&/@(Mean/@SequencePosition[Table[If[PrimeQ[n], 1, 0], {n, 1, 601, 2}], {1, 0, 0}]) (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jul 31 2020 *)
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PROG
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(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
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CROSSREFS
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Cf. A124582, A083370, A134100, A134101, A007510.
Sequence in context: A131610 A211466 A269345 * A129074 A188443 A068411
Adjacent sequences: A134096 A134097 A134098 * A134100 A134101 A134102
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KEYWORD
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easy,nonn
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AUTHOR
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Enoch Haga, Oct 08 2007
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EXTENSIONS
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Definition corrected by Jens Voß, Mar 12 2014
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STATUS
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approved
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