A121495 - OEIS

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

(list; graph; refs; listen; history; text; internal format)

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