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 A099049 Numbers n such that n-1 and n+1 are both prime or both composite. 1
 4, 5, 6, 7, 9, 11, 12, 13, 15, 17, 18, 19, 21, 23, 25, 26, 27, 29, 30, 31, 33, 34, 35, 37, 39, 41, 42, 43, 45, 47, 49, 50, 51, 53, 55, 56, 57, 59, 60, 61, 63, 64, 65, 67, 69, 71, 72, 73, 75, 76, 77, 79, 81, 83, 85, 86, 87, 89, 91, 92, 93, 94, 95, 97, 99, 101, 102, 103, 105, 107 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..70. MATHEMATICA Select[Range[120], AllTrue[#+{1, -1}, CompositeQ]||AllTrue[#+{1, -1}, PrimeQ]&] (* Harvey P. Dale, Sep 01 2021 *) PROG (PARI) for(n=3, 200, s=isprime(n-1)+isprime(n+1); if(s<>1, print1(n, ", "))) CROSSREFS Sequence in context: A075862 A088685 A022299 * A217128 A036668 A260997 Adjacent sequences: A099046 A099047 A099048 * A099050 A099051 A099052 KEYWORD nonn AUTHOR Rick L. Shepherd, Nov 13 2004 STATUS approved

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Last modified September 26 03:54 EDT 2023. Contains 365650 sequences. (Running on oeis4.)