OFFSET
1,1
FORMULA
a(3n+1) = A066509(n+1); a(3n+2) = 1 + a(3n+1); a(3n+3) = 1 + a(3n+2). - R. J. Mathar, Nov 27 2011
EXAMPLE
1309 = 7 * 11 * 17, 1310 = 2 * 5 * 131, 1311 = 3 * 19 * 23.
MATHEMATICA
Select[Partition[Range[10000], 3, 1], AllTrue[#, SquareFreeQ]&&Union[ PrimeOmega[ #]] == {3}&]//Flatten (* Harvey P. Dale, Oct 02 2017 *)
PROG
(Magma) a:=[]; f:=func<n|forall{n+s: s in [0, 1, 2] |IsSquarefree(n+s) and #PrimeDivisors(n+s) eq 3}>; for k in [2..8500] do if f(k) then a:=a cat [k, k+1, k+2]; end if; end for; a; // Marius A. Burtea, Oct 05 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Richard L. Peterson (rl_pete(AT)yahoo.com), Oct 01 2009
EXTENSIONS
More terms from Harvey P. Dale, Oct 02 2017
STATUS
approved