OFFSET
0,2
COMMENTS
Prime for n = 1, 3, 6; semiprime for n = 2, 4, 7, 8, 9, 10, 13, 14, 15, 23, 26. a(n) asymptotic to Phi^A000217(n).
FORMULA
EXAMPLE
a(10) = 1 * 3 * 4 * 7 * 11 * 18 * 29 * 47 * 76 * 123 + 1 = 211913700769 = 349 * 607202581 which is semiprime.
MATHEMATICA
Join[{1}, Rest[FoldList[Times, 1, LucasL[Range[20]]]]+1] (* Harvey P. Dale, Oct 25 2011 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Jonathan Vos Post, Mar 30 2005
STATUS
approved