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

1,1

Comments

Numbers that are in A068780 and in A007674.

Links

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

Example

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

Mathematica

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

Prog

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

Crossrefs

Cf. A002808, A005117, A007674, A068780.

Sequence in context: A114382 A120141 A240593 * A263990 A253810 A084995

Adjacent sequences: A121492 A121493 A121494 * A121496 A121497 A121498

Keyword

easy,nonn

Author

Klaus Brockhaus, Aug 03 2006

Status

approved