A085128 - OEIS

A085128

Multiples of 5 which are members of A002473. Or multiples of 5 with the largest prime divisor <= 7.

5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 75, 80, 90, 100, 105, 120, 125, 135, 140, 150, 160, 175, 180, 200, 210, 225, 240, 245, 250, 270, 280, 300, 315, 320, 350, 360, 375, 400, 405, 420, 450, 480, 490, 500, 525, 540, 560, 600, 625, 630, 640, 675, 700

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

Table of n, a(n) for n=1..55.

FORMULA

a(n) = 5*A002473(n). - Michel Marcus, Aug 15 2017

Sum_{n>=1} 1/a(n) = 7/8. - Amiram Eldar, Sep 22 2024

MATHEMATICA

With[{p = Prime[Range[4]]}, 5 * Select[Range[140], Times @@ (p^IntegerExponent[#, p]) == # &]] (* Amiram Eldar, Sep 22 2024 *)

PROG

(PARI) lista(nn) = {for (n=1, nn, if (vecmax(factor(5*n)[, 1]) <= 7, print1(5*n, ", ")); ); } \\ Michel Marcus, Aug 15 2017