A172458 Nonprimes n such that exactly one of 2n-1 and 2n+1 is prime.
1, 4, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 27, 33, 34, 35, 39, 40, 42, 44, 45, 48, 49, 50, 52, 55, 56, 57, 63, 64, 65, 66, 68, 70, 74, 76, 78, 81, 82, 84, 86, 87, 91, 95, 98, 100, 105, 106, 111, 112, 115, 116, 117, 119, 121, 125, 126, 128, 129, 132, 134, 136, 138, 140
Offset: 1
Links
- Harvey P. Dale, Table of n, a(n) for n = 1..1000
Programs
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Mathematica
Select[Range[150],!PrimeQ[#]&&Total[Boole[PrimeQ[2 #+{1,-1}]]]==1&] (* Harvey P. Dale, Aug 27 2024 *)
Extensions
Edited by Charles R Greathouse IV, Mar 25 2010