A073250 Nonprime squarefree numbers n such that n+1 is also squarefree and nonprime, but not n-1 and n+2.

14, 21, 38, 57, 65, 69, 77, 105, 110, 114, 118, 122, 129, 133, 145, 154, 158, 165, 177, 182, 194, 205, 209, 221, 230, 237, 246, 258, 273, 290, 298, 309, 318, 326, 329, 334, 345, 354, 357, 365, 370, 381, 385, 390, 398, 402, 406, 410, 417, 426, 429, 434, 437

Offset: 1

Author

Reinhard Zumkeller, Jul 22 2002

Keywords

• nonn

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000469, A005117, A073248, A073251, A073249.

Programs

Mathematica

tQ[n_]:=!PrimeQ[n+1]&&SquareFreeQ[n+1]&&(PrimeQ[n-1]||!SquareFreeQ[n-1])&&(PrimeQ[n+2]||!SquareFreeQ[n+2])
Select[Select[Complement[Range[500],Prime[Range[PrimePi[500]]]],SquareFreeQ],tQ]  (* Harvey P. Dale, Feb 14 2011 *)
SequencePosition[Table[If[SquareFreeQ[n]&&!PrimeQ[n],1,0],{n,500}],{0,1,1,0}][[;;,1]]+1 (* Harvey P. Dale, Feb 27 2023 *)