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

1,1

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

Links

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

Formula

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

Example

a(13)=9797

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 *)

Prog

(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

Crossrefs

Sequence in context: A094952 A024526 A213504 * A132657 A161784 A027985

Adjacent sequences: A089578 A089579 A089580 * A089582 A089583 A089584

Keyword

easy,nonn

Author

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

Extensions

Edited by Zak Seidov, Jun 13 2006

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

Status

approved