OFFSET
1,1
COMMENTS
a(n) with n odd must = 2 because 1 is the only odd primorial, thereby the only primorial dividing odd n, and 2 is the smallest prime not dividing odd n. - Michael De Vlieger, Aug 25 2016
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..2310
EXAMPLE
a(6) = 30 because the smallest nondivisor prime 6 = 5 and the smallest primorial dividing 6 is 6 itself. 5 * 6 = 30.
MATHEMATICA
Table[If[n == 1, 2, Prime@If[! MemberQ[#, 0], Length@ # + 1, Position[#, 0][[1, 1]]] (Times @@ Prime@ Flatten@ Position[TakeWhile[#, # > 0 &], 1]) &@ Function[f, ReplacePart[Table[0, {PrimePi[f[[-1, 1]]]}], #] &@ Map[PrimePi@ First@# -> 1 &, f]]@ FactorInteger@ n], {n, 120}] (* or *)
Table[If[OddQ@ n, 2, Function[p, Prime[p + 1] Product[Prime@ k, {k, #[[p]]}]][LengthWhile[Differences@ #, # == 1 &] + 1] &@ PrimePi[FactorInteger[n][[All, 1]]]], {n, 120}] (* Michael De Vlieger, Aug 25 2016 *)
PROG
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Aug 24 2016
STATUS
approved