A121495 Numbers k such that k and k+1 are composite and squarefree.

14, 21, 33, 34, 38, 57, 65, 69, 77, 85, 86, 93, 94, 105, 110, 114, 118, 122, 129, 133, 141, 142, 145, 154, 158, 165, 177, 182, 185, 186, 194, 201, 202, 205, 209, 213, 214, 217, 218, 221, 230, 237, 246, 253, 254, 258, 265, 266, 273, 285, 286, 290, 298, 301, 302

Offset: 1

Author

Klaus Brockhaus, Aug 03 2006

Keywords

• easy
• nonn

Comments

Numbers that are in A068780 and in A007674.

Examples

			21 = 3*7 and 22 = 2*11 are squarefree, so 21 is in the sequence.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A002808, A005117, A007674, A068780.

Programs

Mathematica

q[n_] := CompositeQ[n] && SquareFreeQ[n]; Select[Range[300], q[#] && q[# + 1] &] (* Amiram Eldar, Feb 22 2021 *)

PARI

for(n=1,310,if(!isprime(n)&&!isprime(n+1)&&issquarefree(n)&&issquarefree(n+1),print1(n,",")))