A077682 Squarefree numbers beginning with 6.

6, 61, 62, 65, 66, 67, 69, 601, 602, 606, 607, 609, 610, 611, 613, 614, 615, 617, 618, 619, 622, 623, 626, 627, 629, 631, 633, 634, 635, 638, 641, 642, 643, 645, 646, 647, 649, 651, 653, 654, 655, 658, 659, 661, 662, 663, 665, 667, 669, 670, 671, 673, 674

Offset: 1

Author

Amarnath Murthy, Nov 16 2002

Keywords

• base
• easy
• nonn

Comments

Intersection of A005117 and A217399. - Michel Marcus, Sep 14 2013

Lower density is 1/(10*Pi^2), upper density is 20/(21*Pi^2). - Charles R Greathouse IV, Nov 05 2017

Links

• Muniru A Asiru, Table of n, a(n) for n = 1..6761

Crossrefs

Cf. A077677, A077678, A077679, A077680, A077681, A077683, A077684, A077685.

Cf. A005117, A217399.

Programs

Maple

with(numtheory): select(issqrfree,[seq(seq(6*10^n+k,k=0..10^n-1),n=0..3)]); # Muniru A Asiru, Nov 22 2018

Mathematica

Select[Range[1000],SquareFreeQ[#]&&First[IntegerDigits[#]]==6&] (* Harvey P. Dale, May 19 2012 *)

PARI

is(n)=n>5 && digits(n)[1]==6 && issquarefree(n) \\ Charles R Greathouse IV, Nov 05 2017

Extensions

More terms from Sascha Kurz, Jan 28 2003