OFFSET
1,3
COMMENTS
2 has no isolated divisors. So a(2) is 1.
FORMULA
EXAMPLE
The divisors of 20 are 1, 2, 4, 5, 10, 20. Of these, 10 and 20 are the isolated divisors. So a(20) = 10*20 = 200.
MAPLE
with(numtheory): a:=proc(n) local div, ISO, i: div:=divisors(n): ISO:={}: for i to tau(n) do if member(div[i]-1, div)=false and member(div[i]+1, div)=false then ISO:=`union`(ISO, {div[i]}) end if end do: product(ISO[j], j=1..nops(ISO)) end proc: seq(a(n), n=1..50); # Emeric Deutsch, Oct 24 2007
MATHEMATICA
isoDivs[n_] := Module[{dn = Divisors[n]}, Complement[dn, Union[Flatten[Select[Partition[dn, 2, 1], #[[2]] - #[[1]] == 1 &]]]]]; Table[Times@@isoDivs[i], {i, 60}] (* Harvey P. Dale, Jan 09 2011 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Leroy Quet, Oct 21 2007
EXTENSIONS
More terms from Emeric Deutsch, Oct 24 2007
Extended by Ray Chandler, Jun 24 2008
STATUS
approved