OFFSET
1,1
COMMENTS
Except for 4, all terms are guaranteed to be squarefree.
EXAMPLE
a(5) = 34 because the previous terms being 4, 6, 26 and 626, their product is 390624, and 390624 + 2 = 2 * 17 * 11489, the least semiprime divisor of which is 2 * 17 = 34.
MATHEMATICA
smallestPrimeFactor[n_] := FactorInteger[n][[1, 1]]; semiprimePart[n_] := Module[{p = smallestPrimeFactor[n]}, p*smallestPrimeFactor[n/p]]; a = {4}; Do[AppendTo[a, semiprimePart[2 + Times @@ a]], {15}]; a (* T. D. Noe, Aug 02 2011 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alonso del Arte and Jonathan Vos Post, Aug 02 2011
EXTENSIONS
More terms from Amiram Eldar, Feb 24 2021
STATUS
approved