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A195613 Numbers n with property that n, 2n-1 and 2n+1 are composite. 0


%S 25,28,32,38,46,58,60,62,72,77,80,85,88,92,93,94,102,104,108,110,118,

%T 122,123,124,130,133,143,144,145,148,150,152,160,161,162,164,170,171,

%U 172,178,182,185,188,196,202,203,206,207,208,212,213,214,218,226,235

%N Numbers n with property that n, 2n-1 and 2n+1 are composite.

%C In A000027, if n, n+(n-1) and n+(n+1) are composite, then n is a term of this sequence.

%C Suggestion: there are arbitrarily long sets of consecutive integers, e.g., 632..637, 665..672, 6428..6443.

%t Select[Range[2,1000],!PrimeQ[2#-1]&&!PrimeQ[#]&&!PrimeQ[2#+1]&]

%K nonn

%O 1,1

%A _Zak Seidov_, Sep 21 2011

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Last modified April 8 03:01 EDT 2020. Contains 333312 sequences. (Running on oeis4.)