cp's OEIS Frontend

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

%I A196527 #10 Jul 29 2017 10:02:23
%S A196527 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 A196527 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 A196527 1,1,4,1,1,1,1,1,10,1,2,1,1,1,1,3,8
%N A196527 Greatest common divisor of sums of first n prime numbers and first n composite numbers.
%C A196527 a(n) = gcd(A007504(n),A053767(n));
%C A196527 a(A196528(n)) = n and a(m) <> n for m < A196528(n).
%H A196527 Reinhard Zumkeller, <a href="/A196527/b196527.txt">Table of n, a(n) for n = 1..10000</a>
%e A196527 a(1) = gcd(2,4) = 2;
%e A196527 a(2) = gcd(2+3,4+6) = gcd(5,10) = 5;
%e A196527 a(3) = gcd(2+3+5,4+6+8) = gcd(10,18) = 2;
%e A196527 a(4) = gcd(2+3+5+7,4+6+8+9) = gcd(17,19) = 1.
%t A196527 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 A196527 Cf. A196529.
%K A196527 nonn
%O A196527 1,1
%A A196527 _Reinhard Zumkeller_, Oct 03 2011