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A196527 Greatest common divisor of sums of first n prime numbers and first n composite numbers. 3

%I

%S 2,5,2,1,1,1,1,1,2,1,4,1,7,1,8,1,1,1,1,1,8,7,1,1,1,3,2,1,4,3,1,1,28,1,

%T 1,1,1,1,2,1,1,3,1,1,2,1,1,1,26,1,2,1,1,1,2,1,6,1,1,1,2,1,1,1,1,1,2,1,

%U 1,1,4,1,1,1,1,1,10,1,2,1,1,1,1,3,8

%N Greatest common divisor of sums of first n prime numbers and first n composite numbers.

%C a(n) = gcd(A007504(n),A053767(n));

%C a(A196528(n)) = n and a(m) <> n for m < A196528(n).

%H Reinhard Zumkeller, <a href="/A196527/b196527.txt">Table of n, a(n) for n = 1..10000</a>

%e a(1) = gcd(2,4) = 2;

%e a(2) = gcd(2+3,4+6) = gcd(5,10) = 5;

%e a(3) = gcd(2+3+5,4+6+8) = gcd(10,18) = 2;

%e a(4) = gcd(2+3+5+7,4+6+8+9) = gcd(17,19) = 1.

%t Module[{nn=90,pr,cmp},pr=Accumulate[Prime[Range[nn]]];cmp=Accumulate[ Take[Select[Range[2nn],CompositeQ],nn]];GCD@@#&/@Thread[{pr,cmp}]] (* _Harvey P. Dale_, Jul 29 2017 *)

%Y Cf. A196529.

%K nonn

%O 1,1

%A _Reinhard Zumkeller_, Oct 03 2011

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Last modified April 20 09:59 EDT 2019. Contains 322309 sequences. (Running on oeis4.)