
EXAMPLE

The antidivisors of 5 are 2, 3, and 23 is prime, hence a(5) = 23.
The antidivisors of 7 are 2, 3, 5, and 235 is composite; the antidivisors of 235 are 2, 3, 7, 10, 67, 94, 157, and 237106794157 = 59*547*7346909 is composite; the antidivisors of 237106794157 start 2, 3, 5, 15, 118, 1094, 1709, 4519, 61403, 64546, 7722971, 14693818, 104937727, but the others are unknown, hence a(7) is also unknown.


MAPLE

antidivisors := proc(n) local a, k; a := {} ; for k from 2 to n1 do if abs((n mod k) k/2) < 1 then a := a union {k} ; end if; end do: a ; end proc:
A130846 := proc(n) digcatL(sort(convert(antidivisors(n), list))) ; end proc:
A191648 := proc(n) if n <=2 then 1; else m := A130846(n) ; while not isprime(m) do m := A130846(m) ; end do: return m; end if; end proc: # R. J. Mathar, Jun 30 2011
