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%I #14 Jun 19 2018 05:12:11
%S 1,2,1,1,5,6,7,1,1,2,1,3,1,2,5,2,1,2,1,4,3,2,1,12,1,13,1,14,1,15,1,16,
%T 1,2,1,4,1,1,1,1,1,6,1,1,1,1,1,4,1,10,3,2,1,2,11,2,1,1,1,12,1,2,3,8,5,
%U 1,1,1,1,5,1,2,1,2,3,4,7,2,1,10,3,2,1,1,1,1,1,1,1,1,1,1,31,1,1,32,1,2
%N Greatest common divisor of n and the n-th composite number.
%C a(12) = gcd(12, A002808(12)) = gcd(12, 21) = gcd(2*2*3, 3*7) = 3.
%H R. Zumkeller, <a href="/A064814/b064814.txt">Table of n, a(n) for n = 1..10000</a>
%F a(n) = gcd(n, A002808(n)).
%t Composite[n_Integer] := FixedPoint[n + PrimePi[#] + 1 &, n + PrimePi[n] + 1]; Table[GCD[n, Composite[n]], {n, 100}] (* _T. D. Noe_, Feb 22 2012 *)
%t Module[{nn=150,comps},comps=Complement[Range[2,nn],Prime[Range[ PrimePi[ nn]]]];GCD@@@Thread[{comps,Range[Length[comps]]}]] (* _Harvey P. Dale_, Apr 23 2014 *)
%o (PARI) nextComp(n)= { if (!isprime(n), return(n)); return(n + 1) } { c=3; for (n=1, 1000, c=nextComp(c + 1); write("b064814.txt", n, " ", gcd(n, c)) ) } \\ _Harry J. Smith_, Sep 27 2009
%Y Cf. A002808, A071224.
%K nice,nonn
%O 1,2
%A _Reinhard Zumkeller_, Oct 22 2001
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