A089581 a(n) = prime(2*n-1)*prime(2*n).

6, 35, 143, 323, 667, 1147, 1763, 2491, 3599, 4757, 5767, 7387, 9797, 11021, 12317, 16637, 19043, 22499, 25591, 28891, 32399, 36863, 39203, 47053, 51983, 55687, 60491, 67591, 72899, 77837, 82919, 95477, 99221, 111547, 121103, 126727, 136891

Offset: 1

Author

Norbert A'Campo (nac(AT)member.ams.org), Dec 29 2003

Keywords

• easy
• nonn

Comments

a(n+1) is the smallest squarefree composite number that is relatively prime to the first 2*n prime numbers.

Bisection of A006094. - R. J. Mathar, Jan 23 2013

Examples

			a(13)=9797
		

Links

• Michael De Vlieger, Table of n, a(n) for n = 1..10000

Programs

Mathematica

Table[Prime[2 n - 1] Prime[2 n], {n, 30}] (* Michael De Vlieger, Jul 21 2016 *)
Times@@@Partition[Prime[Range[80]],2] (* Harvey P. Dale, Jan 12 2022 *)

PARI

p=2;q=3;i=1;a=vector(100);for(i=1,100,a[i]=p*q;p=nextprime(q+1);q=nextprime(p+1));a

Formula

prime(2*n-1)*prime(2*n), n=1, 2, 3 ...

Extensions

Edited by Zak Seidov, Jun 13 2006

Typo in PARI program fixed by Zak Seidov, May 19 2010