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 A077678 Squarefree numbers beginning with 2. 12
 2, 21, 22, 23, 26, 29, 201, 202, 203, 205, 206, 209, 210, 211, 213, 214, 215, 217, 218, 219, 221, 222, 223, 226, 227, 229, 230, 231, 233, 235, 237, 238, 239, 241, 246, 247, 249, 251, 253, 254, 255, 257, 258, 259, 262, 263, 265, 266, 267, 269, 271, 273, 274 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Intersection of A005117 and A217394. - Michel Marcus, Sep 14 2013 Lower density is 3/(10*Pi^2), upper density is 20/(9*Pi^2). - Charles R Greathouse IV, Nov 05 2017 LINKS Amiram Eldar, Table of n, a(n) for n = 1..10000 MATHEMATICA s2Q[n_]:=First[IntegerDigits[n]]==2 && 1==Max@@Last/@FactorInteger[n]; Select[Range[274], s2Q[#] &] (* Jayanta Basu, May 22 2013 *) PROG (PARI) is(n)=n>1 && digits(n)[1]==2 && issquarefree(n) \\ Charles R Greathouse IV, Nov 05 2017 CROSSREFS Cf. A077677, A077679, A077680, A077681, A077682, A077683, A077684, A077685. Sequence in context: A106422 A320523 A171549 * A037309 A037315 A110301 Adjacent sequences:  A077675 A077676 A077677 * A077679 A077680 A077681 KEYWORD base,easy,nonn AUTHOR Amarnath Murthy, Nov 16 2002 EXTENSIONS More terms from Sascha Kurz, Jan 28 2003 STATUS approved

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Last modified November 30 18:54 EST 2021. Contains 349424 sequences. (Running on oeis4.)