Some Math and Surtsey

In math I have recently been evaluating sequences in recursive form. 

$Here\; is\; problem\; that\; I\; copied\; off\; Khan$Academy ( and how to solve it ):

$f$ is a function that describes a sequence, and is therefore defined over the positive integers. This is the recursive definition of the function:

$\qquad f(n) = \begin{cases} -3 & \text{if } n=1 \\ -5 \cdot f(n\!-\!1) -7 & \text{if } n > 1.\end{cases}$

Generate the first four terms of the sequence.

$f(1)=$
$f(2)=$
$f(3)=$
$f(4)=$

so f(1)=-3 ( as the table tells us )

and then f(2)=-5*f(2-1)-7=-5*f(1)-7=-5*-3-7=15-7=8

and f(3)=-5*8-7=-40-7=-47

finally f(4)=-5*-47-7=228

I learned about a volcanic island today, named Surtsey, which is off the coast of southern Iceland. The name of the island came from a fire giant from Norse mythology, named Surtr ( Iceland was populated by Norsemen before 1000 AD , and has Norse culture ). It started erupting above surface in November 1964, and has been dormant since about 1966. The first sighting of it erupting was made by a cook on a nearby ship. Iceland claimed it and it is part of Iceland. It has been used as a scientific researching area, by volcanologists ( volcano geologists ) and biologists. The volcanologists studied the eruption and how the island fought the erosion caused by the sea ( among other things ). The biologists studied the founder populations of living organisms that populated the island coming from the outside. The sea continually eroded the Island, but the Eruptions added more and more rock to the island so it grew . After 3 or so years though , the eruptions abated ( and then stopped )  and the erosion damage started making an impact. The Island is getting smaller every year, but once the sea gets to the hard strong ( almost ) non-erodible rock at the core of the Island, the erosion rate will decrease. The living organisms the biologists studied include insects, plants ( including non vascular and vascular ) and birds. The insects and plants were first, and then the birds came, and the way they are connected in a food web is amazing. The Insects eat the plants, then the birds come and the insects provide food for them. There were at first few plant species, but when the birds came and fertilized the soil more , more species were able to survive. Also dead birds provided food for carnivorous insects and decomposers. The Island became protected and only scientists were allowed to go on shore. Everyone who goes on shore now is checked to make sure they are not bringing any new seeds to the island.