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Primes that divide some central trinomial coefficient, A002426.
4

%I #6 Feb 28 2017 01:33:08

%S 3,7,17,19,41,43,47,73,107,109,113,131,173,179,191,193,199,233,269,

%T 277,281,283,293,307,311,347,373,383,401,409,419,421,439,443,457,467,

%U 503,509,521,547,563,569,593,613,617,631,653,673,691,701,709,719,739,743

%N Primes that divide some central trinomial coefficient, A002426.

%C For primes less than 10^6, the density of these primes is near 0.3925.

%H G. C. Greubel, <a href="/A113304/b113304.txt">Table of n, a(n) for n = 1..1100</a>

%t nn=1000; a=b=1; t=Join[{1}, Table[c=((2n-1)b+3(n-1)a)/n; a=b; b=c; c, {n, 2, nn}]]; pLst={}; Do[p=Prime[n]; k=1; While[k<p && Mod[t[[k]], p]>0, k++ ]; If[k<p, AppendTo[pLst, p]], {n, PrimePi[nn]}]; pLst

%Y Cf. A113302 (number of k for which prime(n) divides T(k)), A113303 (least k such that prime(n) divides T(k)).

%K nonn

%O 1,1

%A _T. D. Noe_, Oct 24 2005