OFFSET
0,2
COMMENTS
The new triangles are generated by placing new vertices at the midpoints of each edge in the old triangle.
LINKS
Colin Barker, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (4).
FORMULA
a(n) = 1 if n=0, else 30*4^(n-1).
From Colin Barker, Oct 20 2016: (Start)
a(n) = 4*a(n-1) for n>1.
G.f.: (1+26*x) / (1-4*x). (End)
EXAMPLE
n = 1 is the icosahedron with 30 sides. After dividing each face in 4, there are 120 sides in the next iteration.
MATHEMATICA
{1}~Join~NestList[4 # &, 30, 22] (* or *)
CoefficientList[Series[(1 + 26 x)/(1 - 4 x), {x, 0, 23}], x] (* Michael De Vlieger, Oct 21 2016 *)
PROG
(Python) a = [1] + [30 * 4 ** (n-1) for n in range(1, 24)]
(PARI) Vec((1+26*x)/(1-4*x) + O(x^30)) \\ Colin Barker, Oct 20 2016
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Jonah Caplan, Oct 16 2016
STATUS
approved