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A100319
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Even numbers m such that at least one of m-1 and m+1 is composite.
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3
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8, 10, 14, 16, 20, 22, 24, 26, 28, 32, 34, 36, 38, 40, 44, 46, 48, 50, 52, 54, 56, 58, 62, 64, 66, 68, 70, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 104, 106, 110, 112, 114, 116, 118, 120, 122, 124, 126, 128, 130, 132, 134, 136, 140, 142, 144, 146, 148
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OFFSET
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1,1
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COMMENTS
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Subsequence of A100318. For each k >= 0, a(k+1) = a(k) + 2 unless a(k) + 1 and a(k) + 3 are twin primes, in which case a(k+1) = a(k) + 4 (as a(k) - 1 and a(k) + 5 are divisible by 3).
The even nonisolated primes(n+1). - Juri-Stepan Gerasimov, Nov 09 2009
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LINKS
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G. C. Greubel, Table of n, a(n) for n = 1..1000
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FORMULA
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a(n) = A167692(n+1). - Juri-Stepan Gerasimov, Nov 09 2009
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MATHEMATICA
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Select[2*Range[100], CompositeQ[#-1] || CompositeQ[#+1] &] (* G. C. Greubel, Mar 09 2019 *)
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PROG
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(PARI) forstep(n=4, 300, 2, if(isprime(n-1)+isprime(n+1)<=1, print1(n, ", ")))
(Sage) [n for n in (3..250) if mod(n, 2)==0 and (is_prime(n-1) + is_prime(n+1)) < 2] # G. C. Greubel, Mar 09 2019
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CROSSREFS
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Cf. A100318 (supersequence containing odd and even n), A045718 (n such that at least one of n-1 and n+1 is prime).
Cf. A167692(the even nonisolated nonprimes). - Juri-Stepan Gerasimov, Nov 09 2009
Cf. A005818, A038179, A007310, A038511, A025584.
Complement of A014574 (average of twin prime pairs) w.r.t. A005843 (even numbers), except for missing term 2.
Sequence in context: A308874 A030490 A076639 * A167692 A171689 A163628
Adjacent sequences: A100316 A100317 A100318 * A100320 A100321 A100322
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KEYWORD
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nonn
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AUTHOR
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Rick L. Shepherd, Nov 13 2004
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STATUS
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approved
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