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 A126590 Multiples of 3 or 5 but not both. 3

%I

%S 3,5,6,9,10,12,18,20,21,24,25,27,33,35,36,39,40,42,48,50,51,54,55,57,

%T 63,65,66,69,70,72,78,80,81,84,85,87,93,95,96,99,100,102,108,110,111,

%U 114,115,117,123,125,126,129,130,132,138,140,141,144,145,147,153,155,156

%N Multiples of 3 or 5 but not both.

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

%H Vincenzo Librandi, <a href="/A126590/b126590.txt">Table of n, a(n) for n = 1..1000</a>

%H <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,0,0,0,1,-1).

%F a(n) = a(n-1) + a(n-6) - a(n-7). - _Charles R Greathouse IV_, Oct 11 2013

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

%t 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

%o (PARI) is(n)=isprime(gcd(n,15)) \\ _Charles R Greathouse IV_, Oct 11 2013

%o (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

%Y Cf. A126073, A126592.

%K nonn,easy

%O 1,1

%A _Zak Seidov_, Mar 13 2007

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Last modified December 14 07:03 EST 2019. Contains 329978 sequences. (Running on oeis4.)