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A121495
Numbers k such that k and k+1 are composite and squarefree.
5
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
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
KEYWORD
easy,nonn
AUTHOR
Klaus Brockhaus, Aug 03 2006
STATUS
approved