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, 145157, 154433, 164009

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

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

Example

a(13) = 97*101 = 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 \\ Typo fixed by Zak Seidov, May 19 2010

Crossrefs

Sequence in context: A094952 A024526 A213504 * A132657 A379628 A161784

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

Status

approved