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

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, 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, 1, 1, 4, 1, 1, 1, 1, 1, 10, 1, 2, 1, 1, 1, 1, 3, 8

Offset

1,1

Comments

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

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

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Example

a(1) = gcd(2,4) = 2;
a(2) = gcd(2+3,4+6) = gcd(5,10) = 5;
a(3) = gcd(2+3+5,4+6+8) = gcd(10,18) = 2;
a(4) = gcd(2+3+5+7,4+6+8+9) = gcd(17,19) = 1.

Mathematica

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 *)

Crossrefs

Cf. A196529.

Sequence in context: A146103 A245172 A371751 * A064334 A320032 A270061

Adjacent sequences: A196524 A196525 A196526 * A196528 A196529 A196530

Keyword

nonn

Author

Reinhard Zumkeller, Oct 03 2011

Status

approved