A085132 Multiples of 9 which are 7-smooth.

9, 18, 27, 36, 45, 54, 63, 72, 81, 90, 108, 126, 135, 144, 162, 180, 189, 216, 225, 243, 252, 270, 288, 315, 324, 360, 378, 405, 432, 441, 450, 486, 504, 540, 567, 576, 630, 648, 675, 720, 729, 756, 810, 864, 882, 900, 945, 972, 1008, 1080, 1125, 1134, 1152

Offset: 1

Author

Amarnath Murthy, Jul 06 2003

Keywords

• nonn
• easy

Comments

Equivalently, multiples of 9 with the largest prime divisor < 10.

Crossrefs

Intersection of A008591 and A002473.

Cf. A085125, A085126, A085127, A085128, A085129, A080194, A085131.

Programs

Mathematica

With[{p = Prime[Range[4]]}, 9 * Select[Range[140], Times @@ (p^IntegerExponent[#, p]) == # &]] (* Amiram Eldar, Sep 23 2024 *)

Formula

From Amiram Eldar, Sep 22 2024: (Start)

a(n) = 9*A002473(n).

Sum_{n>=1} 1/a(n) = 35/72. (End)

Extensions

More terms from David Wasserman, Jan 28 2005

Offset changed by Andrew Howroyd, Sep 19 2024