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A061673
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Even numbers n such that n+1 and n-1 are both composite.
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1
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26, 34, 50, 56, 64, 76, 86, 92, 94, 116, 118, 120, 122, 124, 134, 142, 144, 146, 154, 160, 170, 176, 184, 186, 188, 202, 204, 206, 208, 214, 216, 218, 220, 236, 244, 246, 248, 254, 260, 266, 274, 286, 288, 290, 296, 298, 300, 302, 304, 320, 322, 324, 326
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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LINKS
| T. D. Noe, Table of n, a(n) for n=1..1000
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EXAMPLE
| a(3)=50 because 50-1=49 and 50+1=51 and both 49 and 51 are composite.
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MATHEMATICA
| fQ[n_] := !PrimeQ[n - 1] && !PrimeQ[n + 1]; Select[2 Range@ 163, fQ]
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PROG
| (PARI) { n=0; forstep (a=2, 3986, 2, if (!isprime(a+1) && !isprime(a-1), write("b061673.txt", n++, " ", a)) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Jul 26 2009]
(Haskell)
a061673 n = a061673_list !! (n-1)
a061673_list = filter bothComp [4, 6..] where
bothComp n = (1 - a010051 (n-1)) * (1 - a010051 (n+1)) > 0
-- Reinhard Zumkeller, Feb 27 2011
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CROSSREFS
| Cf. A055670.
A025583(n-1) - 1.
Sequence in context: A100393 A133635 A167705 * A072571 A058763 A103079
Adjacent sequences: A061670 A061671 A061672 * A061674 A061675 A061676
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KEYWORD
| easy,nonn,nice
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AUTHOR
| Enoch Haga (Enokh(AT)comcast.net), Jun 16 2001
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