OFFSET
1,1
COMMENTS
Note that for each n=1,...,8, the product of the smallest n-1 distinct prime factors of 2*a(n)+1 is p(n)#/2, where p(n)# is the primorial (A002110) of the n-th prime - and the n-th distinct prime factor >= p(n+1). - Rick L. Shepherd, Jul 06 2002
EXAMPLE
a(4)=577=A000040(106): 2*577+1 = 1155 = 11*7*5*3, 4 distinct factors.
PROG
(PARI) for (n=1, 8, p=1; until(isprime(p) && omega(2*p+1)==n, p++); print1(p, ", "))
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Jun 11 2002
EXTENSIONS
More terms from Rick L. Shepherd, Jul 06 2002
More terms from Don Reble, Apr 15 2003
STATUS
approved