A080672 Numbers having divisors 2 or 3 or 5 or 7.

2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 25, 26, 27, 28, 30, 32, 33, 34, 35, 36, 38, 39, 40, 42, 44, 45, 46, 48, 49, 50, 51, 52, 54, 55, 56, 57, 58, 60, 62, 63, 64, 65, 66, 68, 69, 70, 72, 74, 75, 76, 77, 78, 80, 81, 82, 84, 85, 86, 87, 88, 90, 91, 92, 93

Offset: 1

Author

Cino Hilliard, Mar 02 2003

Keywords

• easy
• nonn

Comments

A020639(a(n)) <= 7; A210679(a(n)) > 0. - Reinhard Zumkeller, Apr 02 2012

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
• Index entries for linear recurrences with constant coefficients, order 162.

Crossrefs

Cf. A020639, A008364 (complement).

Subsequences: A002473, A343597.

Programs

Haskell

a080672 n = a080672_list !! (n-1)
a080672_list = filter ((<= 7) . a020639) [2..]
-- Reinhard Zumkeller, Apr 02 2012

Mathematica

Select[Range[100],Length[Intersection[Divisors[#],{2,3,5,7}]]>0&] (* Harvey P. Dale, Apr 03 2024 *)

PARI

div2357(n)= for(x=1,n, if(gcd(x,210)<>1,print1(x" ")) )

PARI

is(n)=gcd(n,210)>1 \\ Charles R Greathouse IV, Sep 14 2015

Formula

From Charles R Greathouse IV, Sep 14 2015: (Start)

a(n) = 35n/27 + O(1).

For n > 162, a(n) = a(n-162) + 210. [Corrected by Peter Munn, Apr 22 2021]

(End)

For n < 162, a(n) = 210 - a(162-n). - Peter Munn, Apr 22 2021

Extensions

Offset fixed by Reinhard Zumkeller, Apr 02 2012