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Squarefree numbers beginning with 4.
12

%I #17 Mar 05 2021 03:30:29

%S 41,42,43,46,47,401,402,403,406,407,409,410,411,413,415,417,418,419,

%T 421,422,426,427,429,430,431,433,434,435,437,438,439,442,443,445,446,

%U 447,449,451,453,454,455,457,458,461,462,463,465,466,467,469,470,471,473

%N Squarefree numbers beginning with 4.

%C Lower density is 3/(20*Pi^2), upper density is 4/(3*Pi^2). - _Charles R Greathouse IV_, Nov 05 2017

%H Amiram Eldar, <a href="/A077680/b077680.txt">Table of n, a(n) for n = 1..10000</a>

%t Select[Range[499],First[IntegerDigits[#]]==4&&SquareFreeQ[#]&] (* _Harvey P. Dale_, Apr 24 2018 *)

%o (PARI) is(n)=n>40 && digits(n)[1]==4 && issquarefree(n) \\ _Charles R Greathouse IV_, Nov 05 2017

%Y Intersection of A005117 and A217397.

%Y Cf. A077677, A077678, A077679, A077681, A077682, A077683, A077684, A077685.

%K base,easy,nonn

%O 1,1

%A _Amarnath Murthy_, Nov 16 2002

%E More terms from _Sascha Kurz_, Jan 28 2003