A126590 Multiples of 3 or 5 but not both.

3, 5, 6, 9, 10, 12, 18, 20, 21, 24, 25, 27, 33, 35, 36, 39, 40, 42, 48, 50, 51, 54, 55, 57, 63, 65, 66, 69, 70, 72, 78, 80, 81, 84, 85, 87, 93, 95, 96, 99, 100, 102, 108, 110, 111, 114, 115, 117, 123, 125, 126, 129, 130, 132, 138, 140, 141, 144, 145, 147, 153, 155, 156

Offset

1,1

Comments

Numbers n such that (n mod 3)*(n mod 5) = 0 and n mod 15 > 0.

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Index entries for linear recurrences with constant coefficients, signature (1,0,0,0,0,1,-1).

Formula

a(n) = a(n-1) + a(n-6) - a(n-7). - Charles R Greathouse IV, Oct 11 2013

Example

3, 5, 6, 9, 10, 12, (not 15), 18, 20, 21, 24, 25, 27, (not 30), 33, etc.

Mathematica

s={}; Do[m3=Mod[n, 3]; m5=Mod[n, 5]; m15=Mod[n, 15]; If[m3*m5==0&&m15>0, AppendTo[s, n]], {n, 200}]; s

Prog

(PARI) is(n)=isprime(gcd(n, 15)) \\ Charles R Greathouse IV, Oct 11 2013
(Magma) I:=[3, 5, 6, 9, 10, 12, 18]; [n le 7 select I[n] else Self(n-1) + Self(n-6) - Self(n-7): n in [1..70]]; // G. C. Greubel, Mar 06 2018

Crossrefs

Cf. A126073, A126592.

Sequence in context: A281746 A287162 A018900 * A140584 A085705 A187417

Adjacent sequences: A126587 A126588 A126589 * A126591 A126592 A126593

Keyword

nonn,easy

Author

Zak Seidov, Mar 13 2007

Status

approved