login
A089581
a(n) = prime(2*n-1)*prime(2*n).
19
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
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 A379628 A161784
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