OFFSET
0,2
COMMENTS
The construction rules alternate between "vertex to side" (A101946 & companions) and "vertex to vertex" (A061777 & companions). 'Vertex to side' means vertex of n-th generation triangle touches the middle of a side of the (n-1)-th generation triangle. See the link with an illustration. The even terms are the same as in A248969. Note that the triangles overlap.
LINKS
Kival Ngaokrajang, Illustration of initial terms
FORMULA
Empirical g.f.: (3*x^11 + x^10 + 12*x^9 + 5*x^8 + 15*x^7 + 6*x^6 + 15*x^5 + 12*x^4 + 12*x^3 + 5*x^2 + 3*x + 1) / ((x-1)^2*(x+1)^2*(x^2+1)*(x^4+1)). - Colin Barker, Oct 24 2014
PROG
(PARI)
{
c2=0; c3=0; c5=3;
for(n=0, 100,
if (Mod(n, 2)==0,
\\even
if (n<1, a(n)=1, c3=c3+c2; a=6*c3);
c1=n/8+3/4;
if (c1==floor(c1), c2=2, c2=1)
,
\\odd
a=c5;
if (n<=1, c4=12, c4=15);
c5=c5+c4
);
print1(a", ")
)
}
CROSSREFS
KEYWORD
nonn
AUTHOR
Kival Ngaokrajang, Oct 23 2014
EXTENSIONS
Edited. Name and comment reformulated. - Wolfdieter Lang, Nov 04 2014
STATUS
approved