Semiprime: Difference between revisions

=={{header|Elixir}}==

<lang elixir>defmodule Prime do

def semiprime?(n), do: length(decomposition(n)) == 2

def decomposition(n), do: decomposition(n, 2, [])

defp decomposition(n, k, acc) when n < k*k, do: Enum.reverse(acc, [n])

defp decomposition(n, k, acc) when rem(n, k) == 0, do: decomposition(div(n, k), k, [k | acc])

defp decomposition(n, k, acc), do: decomposition(n, k+1, acc)

end

IO.inspect Enum.filter(1..100, &Prime.semiprime?(&1))

Enum.each(1675..1680, fn n ->

:io.format "~w -> ~w\t~s~n", [n, Prime.semiprime?(n), Prime.decomposition(n)|>Enum.join(" x ")]

end)</lang>

{{out}}

<pre>

[4, 6, 9, 10, 14, 15, 21, 22, 25, 26, 33, 34, 35, 38, 39, 46, 49, 51, 55, 57,

58, 62, 65, 69, 74, 77, 82, 85, 86, 87, 91, 93, 94, 95]

1675 -> false 5 x 5 x 67

1676 -> false 2 x 2 x 419

1677 -> false 3 x 13 x 43

1678 -> true 2 x 839

1679 -> true 23 x 73

1680 -> false 2 x 2 x 2 x 2 x 3 x 5 x 7

</pre>