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A174166
Composites n such that 2*n-1 is prime.
2
4, 6, 9, 10, 12, 15, 16, 21, 22, 24, 27, 30, 34, 36, 40, 42, 45, 49, 51, 52, 54, 55, 57, 64, 66, 69, 70, 75, 76, 82, 84, 87, 90, 91, 96, 99, 100, 106, 112, 114, 115, 117, 120, 121, 126, 129, 132, 135, 136, 141, 142, 147, 154, 156, 159, 166, 169, 174, 175, 177, 180
OFFSET
1,1
LINKS
EXAMPLE
a(1)=4 because 2*4-1=7=prime; a(2)=6 because 2*6-1=11=prime.
MATHEMATICA
Select[(#+1)/2&/@Prime[Range[2, 100]], CompositeQ] (* Harvey P. Dale, May 21 2023 *)
CROSSREFS
Cf. A002808.
Sequence in context: A366318 A339424 A175127 * A171401 A120329 A182800
KEYWORD
nonn
AUTHOR
EXTENSIONS
Entries checked by R. J. Mathar, Apr 26 2010
STATUS
approved